The Polish Financial Supervision Authority, or KNF, has asked the U.K. Financial Conduct Authority to keep a close eye on the payments and remittances company Revolut Ltd., after a series of failures encountered by its app users, Reuters reported.

"In connection with the situation which has occurred [payment time out and outages] and the growing scale of the company's operations, the Office of the Polish Financial Supervision Authority has asked its British counterpart, supervising Revolut Ltd. to ensure and maintain increased supervision over the company," the KNF said.

Poland is Revolut's third-largest market in Europe after Britain and France, according to the newswire.

The payment failures were caused by severe latency at Revolut's third-party payment processor, its founder and CEO Nik Storonsky said in a blog post on the company's website on July 1.

Failed payments will be reverted to customer accounts within 72 hours, Revolut said, adding that it is working on moving the process in-house.