[A] In order to generate the JSON file to upload on E-Way Bill Portal, go to the E-Way Bill & GST module (1) from the left-hand panel.
[B] Click on the Eway Bill tab (2) from the top left corner.
[C] Select the Invoice by using the tick box present (3) against every document and click on the Fetch Data button (4).
[D] Validate and put all the mandatory fields present in the data and click on the "Validate & Generate JSON" button.
[E] A new JSON file will get download in your local computer folder, which you can upload on the E-way Bill portal to generate the E-way Bill number against an Invoice.