Hello Duncan,
You have quite some alternatives, i see at least the following:
- mollie https://marketplace.mendix.com/link/component/119366
- imburse https://marketplace.mendix.com/link/component/120699
- paytm https://marketplace.mendix.com/link/component/210690
But basically all gateways with an API should be okay to connect to with mendix.
Hope this helps,
Good luck!