It appears that instant checkout (the current system used by PlayFab) has been deprecated by PayPal since 2017. I believe it would be nice for PlayFab to update it to their newer standards and let us integrate this system with our games.
I understand that this not high priority since many developers do not use your PayPal add-on as mentioned in other posts about sandbox support, but I believe that was because,
- PayPal wasn't supporting credit/debit cards before and instant checkout forced players to create a PayPal account, so developers shied away from it, and
- Playfab hasn't really shown much support for PayPal in the last 3-4 years and developers don't feel confident committing to a monetization platform that lacks support from their backend service provider. Like, sandbox support is one of the highly requested features by developers who use PayPal and for the last 3 years, it has remained in the backlog.
Paypal's newer system, PayFlow, lets users pay for the item/goods with either a PayPal account or a credit/debit card even without logging in. And showing people that you are willing to support the platform with newer updates could be really helpful and can get more developers to work with them.
