Open My Reports → Review expenses, expand the expense, then choose Add document in the Documents section. You can attach a PDF or a JPEG, PNG, HEIC, HEIF, or WebP image as Payment proof, Invoice, Receipt, Contract or agreement, or Other supporting document. Each file can be up to 15 MB.
The file is stored in your ExpenseBot folder in Google Drive and stays linked to that expense. The original receipt or invoice remains the primary document. Adding payment proof does not create another expense, replace the primary receipt, change the amount, or mark an invoice paid.
Expand the expense whenever you need to view its documents or open one in Drive. Use the Documents filter to show expenses that have supporting files. New expense reports can include a Documents & Credits worksheet with the supporting links while keeping the report totals unchanged. If a report row has a supporting document but no receipt, that document is also linked in the report's Link column, labelled Document rather than the receipt's View, so a reviewer can tell a supporting document from an actual receipt at a glance. A receipt link always takes precedence, and links you already put in that cell are never overwritten.