Hi jayeh,
Thanks for posting in the Community!
There multiple reasons why we cannot match the payment to the invoice in QuickBooks Online.
• Dates don't match (or are not close)
• The bank account on the payment is not the same as the bank where the match is located
• The amounts don't match
• The payment has been reconciled
• Multicurrency issue with exchange rates
• Its already been matched to something else
If they don't have the option to find match, just exclude the payment from the Banking tab and mark the invoice as paid manually.
For detailed information you can refer to this link: Find and categorise transactions in QuickBooks.
Please let me know if you have any additional questions. I'm always willing to assist.
