How do I resolve 'Line accounts are missing or invalid' in Dynamics GP?

Overview

You are trying to post an invoice from Dynamics GP to AvaTax but receive the following error "Line accounts are missing or invalid".

Environment

Dynamics GP

Resolution

• In Dynamics GP, go to Setup > Posting > Posting Account.
• Ensure all accounts are populated with values specifically the Item Type (Service, Product, etc) which you are trying to post. 
  • Once accounts are updated, remove line items from invoice, re-add items then click 'Post' on invoice.