1,check amount is incorrect, or has not been provided.
-How much did you paid? If the kid's I-485 is filed together with one of parents'I-485 filing, the fee is $635. If it is filed separately, the fee is $985 (no biometric fee for kid < 14).
See:
我resubmit小孩的485和131时,申请费应该是多少?网上说和父母一起递是635,
现在小孩重新递的还算不算单独递。
-I think it is counted as 单独递. But if you paid $985 originally and USCIS said this amount was incorrect, then your new filing is not counted as 单独递, and you just need to pay $635.
如果算单独递是不是有些表格要重填?
-No. Send the original documents back with correct payment.