I want to start using the e-invoicing feature but am unable to find the option for it. Where can I access e-invoicing in the BUSY?

To Start the Einvoicing feature in BUSY you need to have latest BUSY Release and the feature is available on standard model onwards . To enable einvoicing in BUSY you need to follow the steps 
Step1 Go To Administration menu and click on configuration
Step2 click on features option and go to GST VAT
Step3 make Y on E invoice required option and click on configure
Step4 put the location of your company in from place and Its Pincode 
in Pincode box
Step5 Click on GSP Configuration and select Gsp from which you want to generate E invoice 
Step6 Go to Ewaybill portal and login then go to registration option and click on For GSP
Step7 verify the OTP send in your register mobile number 
Step8 Click on add and select GSP as Webtel electrosoft pvt ltd or Pinnacle finserv advisors pvt ltd 
Step9 add a prefix of 3 digit 
Step10 create a GSP pssword using upper case lower case numeric and special character and password should be under 15 digits 
Step11 reenter same password and add 
Step12 after creating GSP ID copy the user name and paste the same in BUSY 
Webtel user ID or Pinnacle User Id whichever is created and put the password you have created for the gsp in portal then validate and save it 
Step13 Now go to Administration and click on configuration then click on voucher series configuration and select sales voucher and its series then click on Voucher configuration 
Step14 Make Y to the option Generate E invoice after saving and Input transport details option