Invoice is not picking for coding and validation with Vertex/TAX engine enabled.

Although the Vertex/Tax Engine is enabled, when we run the Account Coding program followed by the Invoice Validation program, the invoices are not being picked up for account coding despite all required data being available. However, once we disable the coding step, the invoice validation completes successfully. Requesting your guidance on this issue.

Expectation is when we run all 3 processes,

1)Validate Payables Invoices

2) Partner Transaction Data Extract 

3) Validate Payables Invoices (re-run)

if invoice doesn't have distribution, then it should go for account coding initiation but here it is going to Line/Distribution variance instead of coding initiation.

 Regarding tax calculation, without coding tax should not calculate- vertex configured in such a way we will have tax lines with zero value. when coder enters the distribution and again in next process of all these 3 programs- invoice will get validated. Please advise if you have any insight to resolve this issue.