eBay is buying another payment provider to join forces with subsidiary PayPal.

The company announced Thursday that it will pay around $800 million in cash for Braintree, a payment platform used by many online and mobile startups. Braintree serves such companies as Airbnb, GitHub, OpenTable, TaskRabbit, and Uber. It also offers a mobile app called Venmo, which lets you send money to other people via your mobile device.

eBay expects Venmo to expand PayPay's mobile payments market, which is already forecast to generate sales of more than $20 billion this year.

After the acquisition is a done deal, Braintree will run as a separate service within PayPal. The division will be led by Braintree CEO Bill Ready, who will report directly to PayPal President David Marcus. Braintree's current management team and employees are expected to remain in place, eBay said.

"Braintree is a perfect fit with PayPal," eBay CEO John Donahoe said in a statement. "Bill Ready and his team add complementary talent and technology that we believe will help accelerate PayPal's global leadership in mobile payments. Together, we expect that PayPal and Braintree also will accelerate our leadership in supporting developers who are creating innovative solutions for next generation commerce startups."

Subject to the usual regulatory approvals and other conditions, the acquisition is expected to close late in the fourth quarter