# Add-ons

With Billflow you can sell one-time and subscription add-ons with your plans. These can be shown on the Checkout Form and/or the Customer Portal. Leverage these to start expanding your revenue!

## How it works

### Checkout Form

If add-ons are configured, they will appear below the standard configured products in the checkout form. Your customer is able to select them while checking out and add one-time payments or subscriptions. The total amount will be recalculated and taxes included if configured. [Live example](https://codepen.io/kslung/pen/BaRJwYx)

![Add-ons on checkout](/files/-MfbtjucKDHMIheWT8s9)

### Customer Portal

The customer portal will allow customers to add configured one-times or subscriptions, and manage existing ones. 

One-time add-ons can be added as many times as the user wishes. This feature can be leveraged to create a credit-based pricing model where a customer adds credits to your platform with a one-time payment. 

Subscription add-ons can be turned on or off so you can sell an additional feature or service. 

[Live example](https://codepen.io/kslung/pen/gOWoJOL)

![Add-ons on Customer Portal](/files/-MfbuqsT-we27OLMXHtB)

## Setup Stripe Product

As with standard pricing models, metadata needs to be added to your Stripe products. A new product should be created for each add-on. If you want a single add-on to be available on every tier in your service, then only configure the sb\_service key, and leave out the sb\_tier key. 

Add-ons can also use the [Quantity Management](/how-to/enable-quantity-management.md) feature. Set a unit\_label for the product for Billflow to recognize it as a quantity enabled product. 

Below is the relevant metadata.

| Key         | Value           | Notes                                   |
| ----------- | --------------- | --------------------------------------- |
| sb\_addon   | true            | Enables a product as an add-on          |
| sb\_service | *your\_service* | Configured service to add the add-on to |
| sb\_tier    | *your\_tier*    | Limits the add-on to a single tier      |


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