I modified the Project Request Type in the Admin section and added a user to the list of approvers. However, they still are unable to approve existing Project Requests. Why?
Project Request type approval policy edits do not seem to take effect.
Approval policy edits are not retroactive. So if you have an existing Project Request, and edit the Project Request Types approval policy, the edits do not get applied to the existing Project Requests of that type. The edits will apply to new Project Requests of that type however. The only way to get the new approval policy to take effect is to decline the current pending Project Request, then resubmit it for approval and the new approval policy edits will then be applied.