To find e invoice Generation Option you can follow these steps:
Step 1:Go to Administration menu,
Step 2:Select configuration,
Step 3:Select feature and options,
Step 4:Then click GST/VAT tab,
Step 5:HERE,you can see the Option of E invoice required,enable it and you can configure it.
Step 5:And then you can also enable it from voucher series configuration then click sale then select series then click voucher configuration enable Generate E invoice after Saving, then save this configuration, and now can generate e invoice from BUSY, when you will enter a voucher after saving you can see the option do you want to generate e invoice generate.