Translink: Mobile payment problems frustrate commuters
Angry customers have taken to social media to vent their frustration at problems with Translink's app.
The mLink app allows passengers to use pre-paid tickets on public transport.
However, some customers experienced difficulties on Monday and Tuesday.
Translink say the problem was a result of "supplier capacity issues" which affected operators in the UK and parts of Europe, adding that the app is now working again.
In a statement, Translink acknowledged the purchase of new tickets "was not possible in some cases".
They have urged customers who are experiencing problems to contact them.