Hi Chintan,
I believe this is more a question about the capabilities and settings for the e-commerce plugin you are using. Event Tickets Plus will only send a ticket once the e-commerce plugin processes an order and it is fully considered Completed. In other words, Event Tickets Plus does not look for whether or not you actually received money for the transaction because it relies on the e-commerce plugin to say you did.
It sounds like you were able to find the e-commerce plugin setting that auto-completes your orders. That’s great but, if it is preventing your payment gateway from accepting money, then I would suggest reaching out to the e-commerce plugin support to spot why that’s happening and how to resolve it.
Sorry I do not have a solution for you here, but I hope this at least helps get you pointed in the right direction for getting one.
Thanks,
Geoff