That eliminates one possibility then. Moodle by default does not allow access to localhost, and so if they were on the same server then a work around needs to be employed.
WeBWorK Main Forum
LTI 1.3 Failed to obtain access token from LMS:
This forum has a limit to the number of forum postings you can make in a given time period - this is currently set at 10 posting(s) in 1 day