HOW I CAN ADD QR CODE IN SALES INVOICE ?

If you want to keep using QB Online, utilize this invoicing app as a workaround
https://go.zoho.com/wQI

then use this connector to duplicate data into your QBO account automatically.
https://www.integromat.com/?pc=quickbooks

If you are accepting payments by PayPal or other processors, you can utilize this app to reconcile transactions
https://synder.grsm.io/quickbooks

Otherwise, migrate your data completely to a GAZT approved VAT compliant app.