How to send a box reference within inner txn

The box refs must go on the outer txn, and you can use the simulate on the transaction to find out what references are needed.

I believe this example is what you are looking to do:

This proposal has been withdrawn due to two changes of xGov rules updated on ARC-34 today. Proposals are no longer allowed to represent “Reserving funds to pay for ad-hoc open-source development” and “shall not be divided in small chunks.” I have updated xGov-130 to a new proposal which can be found...

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. PyTeal Documentation