In recent months, thousands of credit card users have received sizeable refunds to their accounts after holidays, concerts and theatre shows were cancelled due to Covid - and many mistakenly believe this refund will count as their payment for that month.
In fact, little-known smallprint means they face late payment fees and black marks on their credit files as major credit card providers include a clause in their terms and conditions that require customers still to make the minimum repayment.
They should not have to pay this if a refund takes the borrower's balance below the minimum payment required, or into the black.
Many credit card holders face late payment fees because they are unaware that refunds do not count towards their monthly payments
But even then, customers could find they receive warning letters that are triggered automatically when payments are missed.
One Money Mail reader says several holiday deposit refunds were repaid to his Tesco credit card, which meant the lender did not collect his direct debit for two months in a row.
He then received a letter claiming Tesco was obliged by the financial regulator to send him a Notice of Sum in Arrears along with debt advice.
'I am an accountant and can deal with these situations but I feel for those who could be badly affected by such a letter,' he says.
A MBNA spokesman says it is made clear that merchant refunds are not accepted as payment. But the lender has waived the late payment charge and her credit file has not been impacted.
James Daley, of Fairer Finance, says: 'From the customer's point of view, a refund onto the card is no different to a payment they made themselves.
'If banks aren't willing to remove these clauses, at the very least they need to be working much harder to make customers aware of them'.
A Tesco Bank spokesman says it is reviewing its systems.