Please note that the document number should not be more than 16 characters as the GST portal will not accept it.
Kindly make changes to the invoice serial number and proceed with downloading the GSTR-1 Report.
Please follow the below mentioned steps on how to change the invoice document number.
Step 1 : Please go to Sales >> Invoices.
Step 2 : Click on the three dots of the invoice number for which it was throwing error.
Step 3 : Make changes to the Invoice document number, including prefix, number and suffix.
Step 4 : Click on Save.
After making changes to the invoice document number, kindly refresh the page and try downloading the report again.
Note : If the error message is showing for multiple invoices, you have to make changes to all the invoices. Currently, there is no option to make changes to the invoice document number in Bulk.