Some Square transactions went unprocessed yesterday thanks to technical problems that also saw the mobile payments firm's Web site go down.
The company's Web site went offline for around one hour while customers also experienced connectivity issues with the Square app.
Despite sharing a founder - Jack Dorsey - with Twitter, the firm has not used the microblogging site to communicate with users but a spokesman has confirmed to tech site The Next Web that "some payments could not be processed".
The outage comes only a fortnight after Square secured a massive deal with Starbucks that will soon see its systems take the strain of processing all card payments for the coffee chain giant.