What Is the Role of the Block Header in the PoW Phase of PoA?

The block header is the target of the PoW mining effort. Miners repeatedly hash the header, modifying a nonce until the resulting hash meets the network's difficulty target.

The header contains metadata like the previous block's hash, a timestamp, and the nonce. Once the difficulty is met, this header serves as the proof that the required work has been performed to earn the right for the PoS phase to begin.