You must have Microsoft Dynamics 365 Business Central version 15.0 or above to get Scaleable Payments.
Before Registration you must have a Stripe Account and the Secret API Key. Change Role Center to Scaleable Payments, there you will find the registration Tile. Tap on registration, fill out all the required fields, click Next, then select your package or get a free trial, click next. In Stripe configuration tile paste your stripe secret API Key.
Check I agree with terms and conditions and click OK.