3: VAA submitted to target chain.
The VAA acts as proof that the guardians have collectively attested the existence of the message payload, in order to complete the final step, the VAA itself is submitted to the target chain to be processed by a receiving contract.
Note: Anyone can submit the VAA to the target chain. The guardians typically do not perform this step to avoid transaction fees. Instead, applications built on top of wormhole can acquire the VAA via the guardian RPC and do the submission in a separate flow.