Shopify offers billing APIs that let you charge the merchants who are using your sales channel. There are two different ways that you can generate revenue through a sales channel app:
Using the Recurring Application Charge API
When the merchant installs your sales channel, use this API to set up their monthly billing. Store the ID for the merchant's recurring application charge for use with the Usage Charge API.
If you don't want to charge a base rate every month, then you can charge $0 per month and use the Usage Charge API to charge commission on every sale.
Learn more about the Recurring Application Charge API.
Using the Usage Charge API
After the recurring application charge has been activated, your sales channel can begin creating usage charges.
Learn more about the Usage Charge API,