So I have done some test sending, and watched my Core Lightning Logs in Start9 while I test.

- When I try and send a payment using RTL, it does not seem to use the xpay plugin, results in an extremely long error message about failed attempts, noting channels that it checked and says had insufficient sats for the send (not true). Perhaps RTL needs an update to have the xpay plugin available to toggle on in RTL in the experimental features section in their service. I also watched the Start9 logs for the send and did not show the xpay plugin being used when attempting the payment.

- When I try and send a payment using Zeus connected using CLNRest, it did not seem to use xpay either. I don't remmeber the error message as it was the first thing I tried and didn't think to take notes, but I believe it was similar to RTL's error message I noted above.

- When I made payments using the Core Lightning user interface accessed via my Start9, payments were successful without issue, and the logs showed the xpay plugin being successfully used.

Hope this is helpful, and also happy to help do additional testing.