I just wanted to share my experience with an LTI error I got, maybe someone runs into the same error. We used a test moodle instance as an LTI provider (3.2) and used an existing one as an LTI consumer (3.1). After setting up the "External Tool" activity, I got the following error message: "Error writing database". Enabling the Developer Mode, it gets a little a bit clearer:
"Data to long for column 'name' at row 1"
In my case our Moodle Platform shortname was just way to long, so I had to shorten it: http://yourmoodle.com/admin/settings.php?section=frontpagesettings