Stripe settings

Stripe settings of Booknetic

If you disable this setting then customers won’t see Stripe choice when booking.
Otherwise, if you activate this choice you must create a new App on your Stripe account.
To create an App, you can get information Stripe Documentation for Building Extensions:

Enter Publishable key you create App and the Secret key to appropriate areas in these settings.

The currency you choose in Settings> Payments must be supported from the Stripe server!