Offer optional features customers can activate on their subscriptions for an additional price.

Add-ons are optional features with their own price and consumption model that customers activate on their subscriptions. They extend a subscription without modifying the base plan — think SSO, SMS channels, or premium support.

How add-ons work

Aspect	Description
Pricing	Fixed base price per billing period, prorated on activation
Charge on activation	Immediate charge for remaining days in current period
Recurring billing	Base price added to the plan's invoice each cycle
Deactivation	No refund — the feature stops immediately
Feature access	The add-on's feature appears alongside plan features

Each add-on maps to exactly one feature. When activated, that feature becomes available through features.get, features.check, and features.list — no different from a plan feature.

Consumption models

Add-ons declare their own consumption model. Boolean add-ons are compatible with any plan. All other models require matching the plan's model.

Model	Description	Compatible Plans	Example
Boolean	Unlocks access, no usage tracking	All plans	SSO, HIPAA compliance
Metered	Included units + overage at period end	Metered plans	SMS: 1000 included, $0.03/extra
Credits	Usage consumes from the plan's credit pool	Credits plans	AI summaries: 5 credits/use
Balance	Usage deducts from the plan's balance pool	Balance plans	Image processing: $0.015/unit

Credits and balance add-ons consume from the plan's shared pool — there's no separate pool for the add-on. If the pool runs out, the add-on's feature is blocked too.

Create add-ons in the dashboard

Go to Add-ons and click Create Add-on. Configure the name, base price, feature, and consumption model. For metered add-ons, set included units and overage rate. For credits, set the credit cost per unit.

The feature dropdown only shows features not already assigned to another add-on. Once created, the add-on is available to any customer whose plan is compatible.

Availability by subscription status

Add-ons can be activated on any subscription with a payment method:

Status	Can activate add-ons
Active	Yes
Trialing	Yes — card was captured during trial checkout
Free plan	Yes — first purchase prompts for a payment method

Manage add-ons

Add-ons are managed through the dashboard and the customer portal. Activation and deactivation are not available via the API or SDK.

Action	Where
Create / archive add-ons	Dashboard → Add-ons
Activate / deactivate	Dashboard (subscription detail) or Customer Portal
List active add-ons	API, Dashboard, or Customer Portal

Feature access

Add-on features work exactly like plan features — no special handling needed:

const customer = commet.customer('user_123')

// Check boolean add-on
const sso = await customer.features.get('sso')
// { access: true, type: 'boolean', enabled: true }

// Track metered add-on usage
await customer.usage.track('sms_messages', 50)

// List all features (plan + add-ons combined)
const features = await customer.features.list()

customer = commet.customer('user_123')

# Check boolean add-on
sso = customer.features.get('sso')
# { 'access': True, 'type': 'boolean', 'enabled': True }

# Track metered add-on usage
customer.usage.track('sms_messages', value=50)

# List all features (plan + add-ons combined)
features = customer.features.list()

customer := client.Customer("user_123")

// Check boolean add-on
sso, _ := customer.Features.Get(ctx, "sso")
// sso.Data.Access == true, sso.Data.Type == "boolean"

// Track metered add-on usage
customer.Usage.Track(ctx, "sms_messages", commet.WithValue(50))

// List all features (plan + add-ons combined)
features, _ := customer.Features.List(ctx)

CustomerContext customer = commet.customer("user_123");

// Check boolean add-on
ApiResponse<Feature> sso = customer.features().get("sso");
// sso.getData().isAccess() == true

// Track metered add-on usage
customer.usage().track(
    TrackParams.builder("sms_messages").value(50).build()
);

// List all features (plan + add-ons combined)
ApiResponse<List<Feature>> features = customer.features().list();

$customer = $commet->customer('user_123');

// Check boolean add-on
$sso = $customer->features->get('sso');
// [ 'access' => true, 'type' => 'boolean', 'enabled' => true ]

// Track metered add-on usage
$customer->usage->track('sms_messages', value: 50);

// List all features (plan + add-ons combined)
$features = $customer->features->list();

# Check boolean add-on
curl "https://commet.co/api/features/sso?customerId=user_123" \
  -H "x-api-key: $COMMET_API_KEY"

# Track metered add-on usage
curl -X POST https://commet.co/api/usage/events \
  -H "x-api-key: $COMMET_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "feature": "sms_messages",
    "customerId": "user_123",
    "value": 50
  }'

# List all features (plan + add-ons combined)
curl "https://commet.co/api/features?customerId=user_123" \
  -H "x-api-key: $COMMET_API_KEY"

Billing behavior

Activation charge

When a customer activates a $50/month add-on on day 11 of a 31-day period (20 days remaining):

	Value
Full price	$50.00
Prorated	$50 × (20/31) = $32.26
Invoice type	`addon_activation`

The charge goes through Stripe immediately with its own invoice.

Recurring invoices

Starting from the next full billing cycle, the add-on base price appears as a separate line in the plan's invoice:

Plan Pro (base)                             $99.00
API Calls: 12,500 (2,500 overage × $0.01)  $25.00

Add-ons
  SMS Channel (base)                        $15.00
  SMS: 1,800 (800 overage × $0.03)         $24.00
  SSO                                       $50.00

Subtotal                                   $213.00

Multi-currency

Add-on prices are defined in USD. For non-USD subscriptions, the price is converted using the plan's exchange rate — the same mechanism used for plan base prices.

Customer portal

Customers can self-service add-ons from the portal:

Available add-ons — see compatible add-ons with pricing
Activate — confirmation dialog with prorated charge preview
Active add-ons — manage active add-ons
Deactivate — instant, no refund

Add-ons whose feature already exists in the customer's plan are hidden from the portal automatically.

Learn more

How Does Billing Work

Consumption Models — Metered, Credits, and Balance explained
Configure Features — Define features that add-ons can unlock
Credit Packs — Another way to extend plan capabilities
Manage Subscriptions — Subscription lifecycle and management
Customer Portal — Where customers activate add-ons

How add-ons work

Aspect	Description
Pricing	Fixed base price per billing period, prorated on activation
Charge on activation	Immediate charge for remaining days in current period
Recurring billing	Base price added to the plan's invoice each cycle
Deactivation	No refund — the feature stops immediately
Feature access	The add-on's feature appears alongside plan features

Each add-on maps to exactly one feature. When activated, that feature becomes available through features.get, features.check, and features.list — no different from a plan feature.

Consumption models

Add-ons declare their own consumption model. Boolean add-ons are compatible with any plan. All other models require matching the plan's model.

Model	Description	Compatible Plans	Example
Boolean	Unlocks access, no usage tracking	All plans	SSO, HIPAA compliance
Metered	Included units + overage at period end	Metered plans	SMS: 1000 included, $0.03/extra
Credits	Usage consumes from the plan's credit pool	Credits plans	AI summaries: 5 credits/use
Balance	Usage deducts from the plan's balance pool	Balance plans	Image processing: $0.015/unit

Credits and balance add-ons consume from the plan's shared pool — there's no separate pool for the add-on. If the pool runs out, the add-on's feature is blocked too.

Create add-ons in the dashboard

The feature dropdown only shows features not already assigned to another add-on. Once created, the add-on is available to any customer whose plan is compatible.

Availability by subscription status

Add-ons can be activated on any subscription with a payment method:

Status	Can activate add-ons
Active	Yes
Trialing	Yes — card was captured during trial checkout
Free plan	Yes — first purchase prompts for a payment method

Manage add-ons

Add-ons are managed through the dashboard and the customer portal. Activation and deactivation are not available via the API or SDK.

Action	Where
Create / archive add-ons	Dashboard → Add-ons
Activate / deactivate	Dashboard (subscription detail) or Customer Portal
List active add-ons	API, Dashboard, or Customer Portal

Feature access

Add-on features work exactly like plan features — no special handling needed:

const customer = commet.customer('user_123')

// Check boolean add-on
const sso = await customer.features.get('sso')
// { access: true, type: 'boolean', enabled: true }

// Track metered add-on usage
await customer.usage.track('sms_messages', 50)

// List all features (plan + add-ons combined)
const features = await customer.features.list()

customer = commet.customer('user_123')

# Check boolean add-on
sso = customer.features.get('sso')
# { 'access': True, 'type': 'boolean', 'enabled': True }

# Track metered add-on usage
customer.usage.track('sms_messages', value=50)

# List all features (plan + add-ons combined)
features = customer.features.list()

customer := client.Customer("user_123")

// Check boolean add-on
sso, _ := customer.Features.Get(ctx, "sso")
// sso.Data.Access == true, sso.Data.Type == "boolean"

// Track metered add-on usage
customer.Usage.Track(ctx, "sms_messages", commet.WithValue(50))

// List all features (plan + add-ons combined)
features, _ := customer.Features.List(ctx)

CustomerContext customer = commet.customer("user_123");

// Check boolean add-on
ApiResponse<Feature> sso = customer.features().get("sso");
// sso.getData().isAccess() == true

// Track metered add-on usage
customer.usage().track(
    TrackParams.builder("sms_messages").value(50).build()
);

// List all features (plan + add-ons combined)
ApiResponse<List<Feature>> features = customer.features().list();

$customer = $commet->customer('user_123');

// Check boolean add-on
$sso = $customer->features->get('sso');
// [ 'access' => true, 'type' => 'boolean', 'enabled' => true ]

// Track metered add-on usage
$customer->usage->track('sms_messages', value: 50);

// List all features (plan + add-ons combined)
$features = $customer->features->list();

# Check boolean add-on
curl "https://commet.co/api/features/sso?customerId=user_123" \
  -H "x-api-key: $COMMET_API_KEY"

# Track metered add-on usage
curl -X POST https://commet.co/api/usage/events \
  -H "x-api-key: $COMMET_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "feature": "sms_messages",
    "customerId": "user_123",
    "value": 50
  }'

# List all features (plan + add-ons combined)
curl "https://commet.co/api/features?customerId=user_123" \
  -H "x-api-key: $COMMET_API_KEY"

Billing behavior

Activation charge

When a customer activates a $50/month add-on on day 11 of a 31-day period (20 days remaining):

	Value
Full price	$50.00
Prorated	$50 × (20/31) = $32.26
Invoice type	`addon_activation`

The charge goes through Stripe immediately with its own invoice.

Recurring invoices

Starting from the next full billing cycle, the add-on base price appears as a separate line in the plan's invoice:

Plan Pro (base)                             $99.00
API Calls: 12,500 (2,500 overage × $0.01)  $25.00

Add-ons
  SMS Channel (base)                        $15.00
  SMS: 1,800 (800 overage × $0.03)         $24.00
  SSO                                       $50.00

Subtotal                                   $213.00

Multi-currency

Add-on prices are defined in USD. For non-USD subscriptions, the price is converted using the plan's exchange rate — the same mechanism used for plan base prices.

Customer portal

Customers can self-service add-ons from the portal:

Available add-ons — see compatible add-ons with pricing
Activate — confirmation dialog with prorated charge preview
Active add-ons — manage active add-ons
Deactivate — instant, no refund

Add-ons whose feature already exists in the customer's plan are hidden from the portal automatically.

Learn more

How Does Billing Work

Consumption Models — Metered, Credits, and Balance explained
Configure Features — Define features that add-ons can unlock
Credit Packs — Another way to extend plan capabilities
Manage Subscriptions — Subscription lifecycle and management
Customer Portal — Where customers activate add-ons

Add-ons

How add-ons work

Consumption models

Create add-ons in the dashboard

Availability by subscription status

Manage add-ons

Feature access

Billing behavior

Activation charge

Recurring invoices

Multi-currency

Customer portal

Learn more

On this page

Add-ons

How add-ons work

Consumption models

Create add-ons in the dashboard

Availability by subscription status

Manage add-ons

Feature access

Billing behavior

Activation charge

Recurring invoices

Multi-currency

Customer portal

Learn more

On this page