The idea is that you would one one redirect URL for your service, for example
https://example.com/redirect_url. You send your customers through the OAuth flow to Stripe and they create an account. Once they are done, we send them back to your redirect URL. There, you identify who they are, usually by using a cookie/session you set before you sent them through OAuth. Based on that, you can then redirect them to the correct URL you wanted them to land on.
For example let's say you have a custom subdomain for each customer. When someone signs up for your service, you calculate their default subdomain and store this in the session or in your database. Then, you send them to OAuth and when they come back you recognize them (with the session) and you know to send them to
https://randomdomain.example.com/ for example.