Once an invoice is submitted for approval, you can find which approval channel it went to in the details view of the invoice and in the summary view of the in-progress tab.
While in the details view of the invoice, scroll down to 'APPROVAL HISTORY' in the header details.
Click the black arrow next to the approval completion percentage. The invoice approval channel name will appear on the right with the approver name as well as its progress along the approval channel.
Summary View in In-Progress Tab
While in the grid view of the In-Progress tab, use the filters or search tab to find the invoice submitted for approval.
Click the 'Thumbs Up' icon to view the approval channel, approver, and progress of the invoice.