REST API for Updating PO Charge Account through Change Order is not working

Summary:

We have created an integration to update PO Charge Account through API. As per business account rules the Variance Account will be same as Charge Account.

The API was failing with error 'The account combination for account type PO Variance Account can't be used because it's disabled.' when the old charge account in PO line is disabled. This is working fine when the old charge account in PO line is active as the Variance account remains the same as old value and does not get updated correspondingly, and the API doesn't call the accounting rules to re-populate the values.