Stripe

You register your OAUth2 app via the Connect->Settings page of the Stripe dashboard:

This page will provide you with both a Development and Production client_id.

You can also register your OAuth2 app callback on the Settings page in the “Website URL” box, e.g.:

However, the OAuth2 secret key is not on this page. The secret key is the same secret key that you use with the Stripe API generally. This can be found on the Stripe dashboard API page:

See more in documentation

https://stripe.com/docs/connect/standalone-accounts