SharePoint 2013 Workflow - ResolvePrincipalInCurrentcontext Unauthorized

I have a simple Workflow that sends an email when an item is approved.

But when the workflow executes I get the following error:

HTTP Unauthorized to https:/mysitecollection/_vti_bin/client.svc/sp.utilities.utility.ResolvePrincipalInCurrentcontext

I already gave App permission to workflow, Im kinda lost on what could be causing this error.

If I give site collection Full Control to the user, it works, but if I give him Contribute permission + Permission to approve the item, it wont work.

What am I missing here?

Thank you in advance!