The Invoice Approval process includes two levels. First-level approval (FLA) starts after a VIM Validator sends an invoice for approval. Additionally, the system calculates default approvers according to the rule determined on the 'Approval Processes Configuration' reference and settings specified in the invoice category.

First-Level Approvers 

We add to a list of first-level approvers:

As VIM Validator you can assign first-level approvers manually. To do that, open a validated invoice and use the button 'Change Approvers'. 

After each of the first-level approvers confirms the invoice, the approval process jumps to the second level.

Second-Level Approvers 

 Second level approvers (SLA) list includes:

In summary, the level shows us who is working on invoice approval. If we are talking about an iteration number, it describes how many times the invoice has been returned for adjustments.

Both FLA and SLA can return the invoice to the pending stage.

Some invoice categories do not require approval. In effect, you can set a maximum invoice amount in the category, and all invoices less than the determined amount will be approved by the Validator.

The member of VIM Approval Override role can approve the invoice at any stage (Validated, Under Approval) of the approval process and bypass all assigned approvers.

As we mentioned before, we can determine first and second-level approvers for each invoice category. Read the article about VIM Invoice Category.