From https://docs.alpenlabs.io/how-alpen-works/bitcoin-bridge

"Apart from the previous Taproot output, the DRT has some metadata attached to it, in the form of an OP_RETURN output, that must be the second output of the transaction in order for the Alpen sequencer to be able to detect the transaction. The OP_RETURN output can be up to 80 bytes long (according to bitcoin standardness policy), and is composed of the following data:

- Magic bytes. These take 4 bytes and are used to identify the bridge.

- Depositor public key (X-only). This takes 32 bytes and are used to validate the DRT, while also necessary for the control block required to spend the P2TR output via the N-of-N Tapscript.

- Execution Layer address. The EL address is the Alpen address where the user wants to receive the BTC on Alpen. It is a 20-byte Ethereum Virtual Machine (EVM) address."

So why could not Citrea do this? #asknostr #op_return