Is there a way to verify if an account has opted in to an ASA during a contract’s execution time?
✔ Solved by SilentRhetoric in post #2
Check if an ASA is opted in by an account with TEAL/Pyteal
Here is the PyTeal section that covers this. Note the way the MaybeValue works.
https://pyteal.readthedocs.io/en/latest/assets.html#asset-holdings