Can I process receipts from multiple business units in one lockbox transmission?

No, the Process Receipts Through Lockbox process runs against a single business unit only. And after you run a lockbox transmission against a business unit, the Import Process ID for that transmission isn't made available to the lockbox import process for other business units.

A single lockbox transmission file consists of one transmission header and trailer. This single transmission can contain multiple lockboxes, but all lockboxes must have the same bank origination number, which identifies the one remittance bank for all data in the transmission.