Linking a payment to a document:
in the Bank form, click the item that should be used to settle the issued invoice,
in the top right corner, click the arrow next to the Services button — the individual options will appear. The most important ones are:
Create payment match — the system will suggest a payment match based on the amount and company; this option is only available if the item does not have the Matched flag checked (navigate to the relevant record, click the Services button, and then select Remove payment match),
Manual payment match — use this when a financial amount arrives in the bank that you want to apply to multiple invoices, or when two invoices have the same amount, or if the document was not found by the Create payment match service,
Automatic payment match — a payment match wizard will open, allowing you to select the criteria by which the Flexi system will match payments; choose one of the available matching options,
WARNING: if there are multiple unmatched bank transactions in the bank with the same variable symbol and amount, automatic matching with a document using the "Automatic payment match" function will not occur.
now go to the Sales – Issued Invoices menu and check whether the document has been settled, as described in the next step,
the item list contains a Payment Status column, which indicates whether a given invoice is paid / partially paid / unpaid / overdue / payment status unrestricted.
A video tutorial on matching payments can be found here: