If you would like to write a letter to confirm that you have received the keys, here is a sample acknowledgment letter for key handover.
I hereby acknowledge the reception of the key(s) associated with [Title of Property], located at [Address], post the completion of all necessary procedures. The key(s) was/were duly handed over to me by [Name] on [Date].
I take full responsibility for the maintenance of the consigned subject(s). All issues shall be dealt with in adherence to the signed agreement.