Have you seen our Support Article that documents how exactly Limited Access works? You can grant Limited Access to your controller to any email address, regardless if they have a Rachio account or not.
Once you’ve added an email to Limited Access, they will be emailed a URL with instructions that can be used to access your controller until the Expiration Date that you set elapses.
If the irrigation professional that you are attempting to provide access to does not have direct access to the email or URL, they would either need to be provided access by the owner or you would need to add their email directly.
One possible workaround you could use would be to add Limited Access to one of your own emails, and then provide that link to the professional directly.
Hope this helps!