How to Restrict a Contingent Workers to be a Line Manager using Workflow Approval

Hello,

We have this requirement to restrict CWK to being selected as Line Manager in Change Manager and Manage Direct Report transactions. It is not working using Autocomplete so we are trying to use Workflow Approval as a workaround but is also not working. We want to auto-reject the transaction if the requestor selected a CWK as Line manager. Is there any possible way to achieve this requirement?

Below is the rule we are trying to work on but it is getting the Worker's Assignment Supervisor.Assignment Number for both current and proposed line manager. We wish to only get the Proposed Line Manager Assignment Number.