Objectives:
The purpose of this text is to discuss the interpretation of the provisions on the payment service provider's obligation to refund regarding unauthorized payment transactions. The subject of the research are the provisions of the Payment Services Act implementing the PSD2 directive in Poland.

Material and methods:
The formal-dogmatic method was applied in the research procedure.

Results:
The result of the research is to propose an interpretation of the provisions governing the obligation to return the amount of unauthorized payment transactions to the payer.

Conclusions:
As part of the results, it was found that, due to the purpose of the legislation, as indicated in its wording and the recitals of the Directive, the obligation to return will be borne by the payer's supplier in principle, except in the event of fraud, intent or gross negligence on the part of the payer. As regards the problem of the burden of proof, a derogation from the general rule resulting from the provisions of the Civil Code consists in shifting the burden of proving that the transaction has been authorized to the supplier.