How to integrate PayPal during user signup to avoid re-entering credentials for future payments?

[mir_rakib]

I am developing an app where users can make payments using PayPal. I want to integrate PayPal into the signup process so that when a user registers, they can link their PayPal account. This would allow them to make future payments without needing to log in to PayPal repeatedly.

Requirements:

1. During signup, users should connect their PayPal account.
2. Save a reference or token securely in the backend to enable server-side payments.
3. Ensure compliance with PayPal's guidelines and security standards. Questions:
4. Which PayPal API should I use to achieve this? (e.g., Billing Agreements, Vaulting, etc.)
5. How do I securely store user information, such as PayPal tokens, to ensure they don’t have to re-authenticate repeatedly and what should I store exactly in server side?
6. Are there any limitations or compliance considerations I need to be aware of? Tech Stack: Backend: C# (.NET Framework/ASP.NET Core). Frontend: React Native.

I saw different API in there docs but I couldn't get exactly what I am looking for. It's quite confusing to me. Any guidance or examples of how to implement this would be greatly appreciated!