You may want to go to the technical team as I am not a developer but I needed to liaise with my hosting company and the JLinked team to get this resolved. There are some hints and tips in the documentation such as only having live the login initially and getting this to work first and then the rest will follow.
My issue lay with security settings and the SSL side of things. Once this was released we had to go through a series of things that are too lengthy to put on here and also would give insight into y site security so I am not able to do so. The contact I had in JLinked was Alex and he was extremely helpful.
I am presuming that you have carefully followed the set up steps on the LinkedIn API side of things as any missed settings can kick out the API working. Worth revisiting these before you jump ahead to Alex but equally if you are unsure the support level from JLinked and their technical team is superb.
When you get the 403 error, are there any messages you're seeing or anything you can post that may help us diagnose the problem?
Beyond that, please try the following:
* Disable all JLinked Profile plugins and test again
* If that works, re-enable one plugin at a time for only the extensions you use (don't enable the JomSocial profile plugin if you don't have JomSocial enabled). Try logging in after each one you enable and see if it works. If not, let us know which plugin stops it from working.
I can't see the SCLogin module anywhere on the front-end of your site. Can you PM me a link to a page where we can see it or specific instructions on how we should enable it? We don't like making modifications to sites, so would like your input on how you have things configured already.
As for the error page you show, one thing you can try is to go to the Joomla Global Configuration and set Error Reporting to "None" and turn off Gzip compression. Also, disable any 'optimizer' plugins you may have enabled. Then, that page may show a real error message that will help diagnose the issue.
Ahh, glad you got that going. Not sure why that would be necessary, but there is a lot of communication back and forth between your site and LinkedIn. If sh404SEF alters those links in a bad way, it could definitely cause a problem.
For JLinked operation, we really don't have any front-end URLs except for the registration page, which shouldn't really need to be SEF'd anyways, so you shouldn't have any drawbacks from disabling sh404SEF for JLinked.
If you run into any other issues or need anything else, just let us know!