To to see the option for Alt+X to cancel an invoice, you need to follow the below steps:
Step 1: You need to open that e invoice sales voucher in Modify mode by using Steps: Transactions, Sales, Modify,
Step 2: then put the bill number of that particular e invoice, click OK, and open it.
Step 3: After you open the sales invoice voucher window, you will see a cancel option at the top of the screen. Click on that option to cancel the sale invoice in BUSY,
Step 4: and then it will ask for narration. Put cancel narration,
Step 5: and then they will ask if you want to cancel from the GST portal. Also, click Yes to cancel from the GST portal.