Apple customers who were planning on adding their credit cards to the Apple Pay mobile payment system may have to wait a little longer.

Apple’s mobile payment service experienced an outage starting at 4 a.m. EST Wednesday, according to the company’s system status page. While some customers are still able to add their credit cards, those with Visa credit and debit cards were prevented from adding them to the mobile wallet.

As of 11 a.m. EST, Apple still listed the service as partly down. Customers who already have Visa cards loaded onto Apple Pay should still be able to make mobile payments with an iPhone or Apple Watch, as well as in apps via the latest iPad models.

Apple Pay launched in 2014, coinciding with the debut of the iPhone 6. Customers who opt in to the service can load a credit card onto their device and make payments in-store via wireless near-field communication technology or in apps that support it.

To date, nearly 1,000 banks and credit unions support Apple Pay in the U.S. while 15 banks in the U.K. do so. Apple Pay is also available in Canada and Australia via American Express. Later in 2016, Apple will roll out Apple Pay to China in partnership with China UnionPay, the national credit card network there.

While Apple Pay and other mobile payment services such as Android Pay and Samsung Pay were initially touted as a payment option that could replace credit cards, their uptake has been relatively slow. Apple Pay sees about 15 million to 20 million users per month in the U.S., while Google’s Android Pay sees about 5 million to 15 million monthly users worldwide, according to a Piper Jaffray research note released Tuesday.