Receipts and what makes one valid

Which costs need one

Every overnight stay claimed at its actual cost. The checklist item is "Every overnight stay has a receipt", and it blocks approval.

Beyond that, attach a receipt to anything you would not want to justify from memory. The threshold is not really a rule, it is a question of what you can defend later.

Per diems need no receipt. That is the entire point of a per diem: it is a flat amount you may claim without proving what you spent.

What has to be on it

A receipt has to show what was bought, when, for how much, and from whom. A card statement line is not a receipt: it proves you paid someone, not what for.

For foreign-currency receipts, record the exchange rate too. The checklist requires one for every foreign-currency cost.

Attaching them

Attach receipts to the cost they belong to, not to the trip in general. A pile of images attached to the trip is a pile somebody has to match up by hand later, probably you.

Receipts are stored encrypted, like everything else in Files.

They freeze at approval

Once the trip is approved and sealed, the receipts are part of a sealed report. You cannot swap one out.

If a receipt was wrong or missing, revert the approval, fix it, and resubmit. The superseded report is kept, so the record shows there was an earlier version rather than pretending the correction had always been the case.

The one that gets forgotten

A hotel invoice that includes breakfast is two things at once: the accommodation cost, and evidence that breakfast was provided. Attaching the receipt without ticking the breakfast reduction on that day is the most common way a trip ends up overstated. See Per diems, meals and overnight stays.