what's the difference between a receipt and a bill

They're different points in time, and Talisk treats them differently on purpose.

A bill is something you still owe: an obligation. It sits in accounts payable until it's paid, so it shows up in what you owe suppliers and in your aging report.

A receipt is proof of a payment you've already made. There's nothing outstanding, so it never touches accounts payable: it's recorded as the expense it is.

Getting this wrong is a common source of double counting: if you enter a receipt as a bill, you create a payable that doesn't exist, and your books say you owe money you already paid.

Both live together under Ledger › Expenses, tagged so you can tell them apart, with an Unpaid filter for the bookkeeper's view of what's genuinely still outstanding.