Update Leads on rest api only creates new leads

Hi, I am trying to use rest api with Update leads API.
Only when i define action=createOrUpdate it creates a new lead each time.
When I try updateOnly it does nothing.
I update a lead with an id that is deifned in the database and for some reason it is not found in the database.

Any ideas why? Is there some logs or some place i can check to find out why the lead i tried to update was not found?

Thanks