To add/create GST invoice you need to have GST number. Please make sure you have added your GST number in the Company details.
Then, the when creating product it should be added with tax.
If the tax is included in product, then only invoice will be created with tax.
To add product with tax,
Step 1: Please go to Products & Services.
Step 2: Click on +New Item.
Step 3: Enter product level details, including Tax/GST percentage.
Step 4: Click on Add Item.
Once the product added with GST, please refer to the below article to create an GST invoice by adding the same product added with GST.
NOTE : You need to have GST number, in order to create GST bill.



