If you are filing married jointly and have 1 dependent then 4200 is the correct amount. Did you get the 4200 third stimulus payment last year ? Did the IRS only send one spouse the letter stating 2100? If so you still had to enter the 4200 you actually got even if you did not get the second person's reminder letter. So if you had a credit on line 30 of the form 1040 and you did get the full credit in advance then the IRS would adjust the return accordingly ... you can either have the credit or the advance but not both.
