British neobank Monzo has reinstated a popular feature for its current account, debit top-ups via card, Android and Apple Pay, but warned customers that the feature may not be “sustainable” for the bank.

In a statement on the Monzo blog posted today, the bank noted that it had brought back the debit top-up feature — adding money to a Monzo account via a card from another account — due to customer feedback, but also stated that the feature was expensive for the bank to offer, just as it is expensive for merchants to accept card payments. 

Monzo said in the blog post, including the bolded text:

However, supporting this feature is also incredibly expensive for us. Every time you top up from another debit card, Monzo has to pay processing fees, calculated at a percentage of the amount you top up. On average, this costs us around £24 per customer each year.

Monzo followed the announcement of this cost with a request that customers only use the feature for “last-minute emergencies,” as it “isn’t sustainable for us to keep covering the costs if everyone only uses top ups to add money to their Monzo accounts.”

Read more at Monzo and Finextra.