My purchasing department is always changing the total amount in a PO and the difference needs to go through an approval process. Any suggestions on what to do here they usually change the PO amount 12 times .

Create a new field called "Last Approved Amount" on the PO. Use a set field value action upon entry into the approved state to set this field to the {total} field from the PO Add a transaition to the Approved state with the criteria of Last Approved Amount is NOT EQUAL to {total} Transition after record submit Transition to the pending approval state (or a new pending approval state called PO AMOUNT CHANGED)

But how would this not leave the workflow once it is approved ?

There is a checkbox on the state "Do Not Exit Workflow", it should prevent your record from exiting the workfow

Also once you add a transition out of the approved state then records won’t ever leave the workflow as well

We have a solution very similar to that @MGBC It works well, only diff is that we only trigger the re-approval after some % change is reached