Difference between GSTR-1 and GSTR-3B

 an invoice to Gstr 1 after filing?

To manually upload invoice to GSTN, follow the steps below:

1. Step 1: Login to your GST account. GST Login.
2. Step 2: Select the month for which you wish to upload GST invoices. ...
3. Step 3: Select GSTR-1 Return and Click on Prepare Online. ...
4. Step 4: Upload B2B Invoice Details. ...
5. Step 5: Upload B2C Large Invoice Details.

Just add invoice in GSTR 1 of Sep 21 but do not consider in Aug 21. Maintain track of variances between returns if questioned by dept. later