Questions:

If at the verification stage, a particular field (Like Invoice number) is empty, then how to route the document/batch again back to the verification stage and should not be able to be sent to the next stage.

Solution:

From the Project->Project Properties->Workflow->under Advanced workflow-> create an additional custom stage and place it right after Verification (and before the Export stage). Let's name this stage as "Send Back to Verification If Invoice Number is Empty"

Then inside this stage, the Entry Conditions is as default Always

For the Exit Routes add the Stage... and choose Verification

And in this stage add this rule where the "Field value satisfies the expression" that the InvoiceNumber is equal to blank

Then when the operator tries to complete the task and if the Invoice Number field value is blank/empty, FlexiCapture will automatically resend it back to Verification