Krishika Sahay start with your charge cable and charger. Make sure that it is in good working condition and that it supplies the power needed for your Xiaomi Redmi Note 6 Pro. After that check the charging port. make sure there is not dirt/lint etc in it. a few puffs of compressed air should clean it out. After that you will have to start thinking about disassembling your phone and check with a multi meter that the charging port is properly connected to the board. Replacing the battery will also be necessary to ensure that is not the issue.