Form 67 queries

Pls explain.

Actually I have income from US... is I got form F 1042-S which shows the amt of income + withheld tax amt... the said form is for 2020... so my doubts are -
1) while claiming credit I will be able to claim only till period dec 2020 and remaining i.e related to Jan to mar 2021 will be claimed next yr ?
is this correct ?
2) the gross amt of income shown in form F 1042 S doesn't match with gross amt which I actually received i.e gross amt as per the invoices. so which amt to consider while claiming credit of foreign tax ?
3) the rate of tax withhold is 15% . however in some invoices the amt is calculated taking rate lower than 15%. so what to do in such case ?

1) In us and England FY IS JAN TO DEC
2)IF THERE IS MISMATCH YOU HV TO FIND OUT THE ITEMS WHICH ARE MISSING
THEN 1042 FORM WILL BE CORRECT
3)PLS GÒ THRU EACH INVOICE OR SEND DERAILS AT CONTACTAT @ EASYACCOUNTINGAUDITTAX.CO.IN
Ì CAN HELP YOU OUT CERTAINLY.