I am trying to understand what is in a transaction specifically the payload. While the documentation references the term payload, it is not explicit/clear about what exactly it is. It seems to include the block number and block hash for determining mortality but what else does it include? I need an "explain payload to me like I was 5", I can sort out the details but I need a clear, conceptual model of what is in the extrinsic/transaction. Furthermore, the payload is then signed and then serialized. Was it not serialized before being signed?
This is the documentation I have looked at: https://wiki.polkadot.network/docs/build-transaction-construction
Is the payload, this information? If so, the metadata is already encoded, so does it get encoded again?
Address: The SS58-encoded address of the sending account. Block Hash: The hash of the checkpoint block. Block Number: The number of the checkpoint block. Genesis Hash: The genesis hash of the chain. Metadata: The SCALE-encoded metadata for the runtime when submitted. Nonce: The nonce for this transaction.* Spec Version: The current spec version for the runtime. Transaction Version: The current version for transaction format. Tip: Optional, the tip to increase transaction priority. Era Period: Optional, the number of blocks after the checkpoint for which a transaction is valid. If zero, the transaction is immortal