Oct 19 (Reuters) - Payments services provider Billtrust said on Monday it will go public through a merger with blank-check firm South Mountain Merger Corp in a deal valued at $1.3 billion, including debt.

Billtrust, which provides payment services for transactions between businesses, said the combined firm will list on the Nasdaq Stock Market and have a cash balance of around $200 million.

A blank-check firm, or a special purpose acquisition company (SPAC), is a shell company that raises money in an IPO to merge with another company, typically within two years.

The SPAC model has become an increasingly popular route to the public markets this year over a traditional IPO, allowing companies to skip the associated costs and regulatory requirements.

Earlier this year, Softbank-backed home-selling platform Opendoor Labs Inc had agreed to go public through a SPAC merger, while U.S. insurance startup Clover Health had inked a $3.7 billion deal to list through a merger with Social Capital Hedosophia.

Citigroup Inc is advising South Mountain on the deal, while JP Morgan is advising Billtrust.

(Reporting by Ambar Warrick in Bengaluru; Editing by Krishna Chandra Eluri)