Eligibility requirements
To use third-party subscription apps, your store must meet the following requirements:
You must be using one of the following payment gateways:
Stripe, which is only available to some merchants
In case you are looking to activate these gateways later you can setup Shopify Payments in test mode for now: https://help.shopify.com/en/manual/payments/shopify-payments/testing-shopify-payments