Issue in Create transaction of genie business

We have verified the following in UAT:
Transactions without customerId complete successfully
Any transaction with customerId fails at Pay Now
This happens even with tokenize=false

This confirms that customer-linked transaction capability is not enabled for our merchant in UAT.

Please enable and confirm:
Customer-linked payment flow for our merchant
Customer -> transaction routing
(Optional) Token vault linkage for future COF
Test reference:
Working transaction (no customerId):
Failing transaction (with customerId): 6943a6c4efc64b42045701c2