Recording a petty cash expense
Open the project, tap Payments on Project Home, then Petty Cash.

Petty Cash sits alongside Transactions and Parties. The Petty Cash screen lists each petty cash account on the project with its current balance on the right.

The Petty Cash list, with a balance against each account. Use the search box at the top to find an account quickly once several are running.
Open an account to record what was spent and what it was spent on. Keeping site expenses here rather than in a notebook means they reconcile against the project rather than being reconstructed at month end.