American Express and Groupon have become the latest investors in mobile payments company SumUp, as part of a double digit million euro (i.e., anywhere from €10-99m) round of funding.

The two companies join existing investors including b-to-v Partners, Shortcut Ventures, and Tengelmann Ventures, which contributed further funding on top of the $20m (£13m) invested as part of a Series A funding round last August.

Its probably not a coincidence that three months ago, SumUp signed a deal with American Express enabling it  to process AmEx card payments for the first time.

“We are delighted to bring on Groupon and American Express as financial investors,” said SumUp CEO Daniel Klein. “Both companies share our vision and our commitment to empowering small businesses. As one of the world’s largest card issuers, American Express is at the forefront of driving innovation in payments. Groupon has proven that it is possible to build a company serving millions of small merchants worldwide in a short period of time.”

According to SumUp, it will use the money to fund further building out its end-to-end payment solution and continued expansion into new territories, with some of the funds also going towards the development of new services.