You can review the credit note of the downloaded invoice number to check if it doesn't exceed 16 characters and, make sure it contains letters, digits, hyphen forward slash, i.e. (A to Z, 0 to 9, -, / ). Backward slash (\) is not permitted.
To locate the invoice number, here's how:
Click Reports in the left pane.
In the Go to report search box, type Transaction List By Customer and run this report for the same period as the GSTR1.
Locate Invoices that have non-permitted special characters and that are over 16 characters in the No. column.
Open the transaction.
Edit or enter a new Invoice number.
Click Save and close.
However, if the invoice number is correct, let's perform some basic troubleshooting to figure out if the browser is causing the error to happen. We can start by logging into your QuickBooks account through a private browser.
Here are the shortcut keys depending on the browser you're using:
Google Chrome: press Ctrl + Shift + N
Mozilla Firefox: press Ctrl + Shift + P
Safari: press Command + Shift + N
If everything looks fine, return to your default browser and perform a clear cache to remove temporary internet files on your computer. Using a different browser is a good alternative too.