Reuters) - Affirm Holdings Inc beat Wall Street estimates for quarterly sales on Thursday, helped by a growth in volumes of goods sold through its buy now, pay later (BNPL) platform, coupled with a rise in the number of merchants and active consumers. Shares of the company jumped 19% to $109.61 in extended trade.BNPL firms like Affirm earn from charging merchants a fee to offer their customers small, point-of-sale loans which are paid back in interest-free installments over a period of time, bypassing credit checks. The company’s gross merchandise volume (GMV), a metric used in the e-commerce sector to measure transaction volumes, rose 106% to $2.5 billion during the quarter.Active consumers surged by 97% to 7.1 million during the quarter while active merchants grew 412%, Affirm said. Total revenue rose to $261.8 million during the fourth quarter ended June 30, from $153.3 million, a year earlier. Analysts on average had expected revenue of about $225 million, according to IBES data from Refinitiv.