CPIN - Common Portal Identification Number is generated along with the GST payment challan. It is a 14 digit unique number to identify the challan. The CPIN is valid for 15 days.
CIN - Challan Identification Number is a 17-digit number consisting of a 14-digit CPIN plus a 3-digit bank code. CIN is generated by the authorised banks/RBI when payment is actually received and credited to the department. CIN is communicated to the taxpayer as well as the department after the payment of GST.