Financial institutions and retailers are developing a bigger appetite for Apple’s mobile payment option, and a Greater Des Moines-based payment processor is getting a slice of that business. The Members Group has now enrolled 25 percent of its card issuer clients in Apple Pay, the Clive-based payment processor said today, which accounts for roughly 10 percent of all financial institutions enrolled in Apple Pay. TMG leaders expect nearly half of its clients will be enrolled by midyear. Overall, Apple Pay adoption by financial institutions grew by 21 percent from March to April. “Early-adopter clients have been ecstatic about rolling out Apple Pay and report similar enthusiasm for upcoming solutions like Samsung Pay and others,” said Brian Day, TMG’s director of digital strategy. Among retailers, Apple recently announced it has enrolled Express clothing stores as an Apple Pay partner, and may land Trader Joe’s and the Home Depot as well, PYMTS.com reported.