Update: Found an article on this site which described that LTI can fail if the LTI Publisher uses a custom favicon in their Cartridge URL. Our LTI Publisher uses custom favicons. So we removed it and we were able to access the Publisher's course 1 time successfully.
In our testing, as a learner, we logged in accessed the course and then logged out. However, we are unable to access the course again. The error we are getting this time is:
I will ask the Moodle Universe, is there a piece of code that we should be adding onto the end of the Tool URL so the LTI Publisher will accept a learner's multiple attempts to access the course? We have read that we should/could put a '/' at the end of the Tool URL...but is there something that will allow for the Publisher's site to allow multiple accesses to the course by the same learner?
Any help is gratefully appreciated!