I received a C12 form reducing my refund from $1515 to $315 and I am unsure why? What do I do?

[SweetieJean]

The $1200 reduction may represent a disallowed Recovery Rebate Credit.  Any first and second Economic Impact Payments (stimulus payments) that were issued to you reduce the amount of any 2020 Recovery Rebate Credit that you claimed.   Call the number on the CP12 notice for more information.

Understanding Your CP12 Notice | Internal Revenue Service (irs.gov)

2020 Recovery Rebate Credit | Internal Revenue Service (irs.gov)

[VolvoGirl]

A common adjustment is if you claimed the Recovery rebate credit on 1040 line 30 when you already got the Stimulus payment or got the second one after you filed or reported the wrong amounts or entered them in the wrong box.  Do you have the 1200 on 1040 line 30?