How does matching work?
The link is the bridge between two truths: what you invoiced and what is actually in your account. Without that bridge you have two lists that are both correct and together say nothing.
The distinction from VAT matters because it determines how serious a backlog is. A pile of unmatched lines is annoying and blurs your view of open items, but it changes nothing about what you have to pay. That is a reason to do it calmly and properly instead of in a hurry.
With differing amounts, splitting is the right move. A payment of €3,625 on an invoice of €3,630 is not an invoice of €3,625; it is a payment with five euros of bank charges or a remainder that is still open. Which of the two it is determines what your customer still owes.
Where is matching in the law?
For this term there is no statutory basis to refer to, and that is not an omission but the state of affairs. It is a term from bookkeeping practice, not a legal obligation with its own article.
What does apply sits one level higher: under Article 52 of the Dutch General State Taxes Act (Algemene wet inzake rijksbelastingen, AWR), your bookkeeping must be verifiable within a reasonable time. How you set that up is not prescribed by law.
What does basestep do with matching?
basestep warns about unmatched bank lines and states explicitly that it is a cash matter and not a VAT matter, so a warning does not lead to panic about your return. You split partial payments instead of rounding them.
All calculations, explanations and signals in basestep are calculation support and instruction, not tax or legal advice. Amounts are estimates based on your own input; the Dutch tax authority (Belastingdienst) sets the assessment.
Where does it go wrong with matching?
The two mistakes you run into most often in practice with this term, and what they cost you.
Rounding to make it balance
A difference of a few euros has a cause: bank charges, a partial payment or a correction. Polishing it away costs you the view of what is still open.
Thinking it affects your VAT
VAT depends on the invoice and the period. A backlog in matching is a problem for your receivables management, not for your return.
Further reading
Three places this term is tied to, inside this glossary and beyond.