Zend certified PHP/Magento developer

Free method is not displaying for custom discount

I have developed a module for custom discount on M2 checkout page. It is working fine but when grand total is 0 that time I am unable to place an order. All method is showing “This payment method is not available ” also free payment option is not showing. In the response of payment-information end point I am not getting free method. Please help me , I want to display free method if grand total is 0. For magento coupon free method is displaying but only for my custom discount module it is not displaying. Please help me out to solve this issue.

Thanks & Regards,
Mousam