Returns a transaction for depositing additional ETH to an active 0x02 validator. Deposit amount must be at least 1 ETH.

How to sign the compound tx

If funding_address is not provided, the API uses the validator's withdrawal address as the funding address by default. The transaction must be signed using the withdrawal address.
If funding_address is provided and it's a different address from withdrawal address, the transaction must be signed using the specified funding address.

signature and withdrawal_credentials are "all zeros"

When parsing the call data of the serialized transaction, you will notice that both signature and withdrawal_credentials are all-zeros. This is normal and expected for compound transactions. Here’s an example for reference