PayZapp was the app which used to use for all of my bill and utility payments.
Recently they completely dropped the old app and made a new app, even after the new changes the app used to work fine. But after the latest update the app is no longer working and it says ER015 when opening the app which means SAVE_FOR_FUTURE_DISABLED as per this website https://docs.zetaapps.in/display/PWP/Error+codes
I also found the below threads not to update the payzapp app to the latest version on rooted phones.
https://www.technofino.in/community/threads/information-rooted-phone-users-do-not-update-payzapp.11533/
https://www.desidime.com/discussions/rooted-phone-users-do-not-update-payzapp

Version PayZapp 1.0.0.230424-56.10 used to work fine butin version PayZapp 1.0.0.230420-56.05 it completely stopped working.
https://apkcombo.com/payzapp/com.hdfcbank.payzapp/old-versions/

Native code debugging is enabled.
Tried enabling and disabling Exploit protection compatibility mode.

Based on what you're describing, it sounds like their app now requires a Google certified OS, which GrapheneOS isn't.

They'd need to not do that anymore, or optionally whitelist GrapheneOS. There is a guide meant for developers to implement this for their apps, though it is unlikely they'll do it, I'm afraid:

https://grapheneos.org/articles/attestation-compatibility-guide

I wan to be clear that I don't know for sure that this is what's happening, it just sounds the most plausible explanation based on what you're describing.

The only other thing I can think of is to go to Settings > Security and disable Secure Exec Spawning, reboot, and try again.

If it still doesn't work, re-enable it and reboot.