Query relating to finacial credit note

Ajnas (Student) (844 Points)

03 February 2021  
Mr Y sold goods on credit Rs. 10000+18% GST to Mr. X, and then Mr Y allowed entire  Rs. 10000+18%  as cash discount
1. Is any issue on supplier for issuing financial credit including gst?
2.If GST Rs. 1800 is already paid to Mr. Y, then remaining Rs. 10000 is allowed as cash discount then receipent is required to reverse the itc?