Testing prerequisites You need two Moodle sites (localhost is fine) - one called 'platform' and one called 'tool' In the tool site admin settings: Enable enrol_lti and auth_lti plugins Enable "Allow frame embedding" In BOTH sites: Go to "Administration > Security > HTTP security" and clear all values from the 'curlsecurityblockedhosts' admin setting and save (to permit localhost-to-localhost calls) Testing {issuer, client_id} uniqueness during platform registration Now, in the tool site, go to "Admin > Plugins > Enrolment plugins > Publish as LTI tool > Tool registration Generate a new dynamic registation URL by clicking the button Copy the URL using the copy to clipboard feature Now, in the platform site, login as admin Go to "Admin > Plugins > Activities > External tool > Manage tools" Paste the dynamic registration URL you copied into the text field and click "Add LTI Advantage" When the page reloads and you see the tool, go back into the tool site tab Reload the page Under "Registered Platforms" below, Verify the following: You see a single platform registration entry You see a single deployment for that registration Now, generate another registration URL above and copy it. Go back to the platform site tab In manage tools, enter the URL you just copied into the field and again click "Add LTI Advantage" You'll be presented with upgrade options, but just select "Register as a new external tool" When the page reloads and you see the tool, go back into the tool site tab Reload the page Under "Registered Platforms" below, Verify the following: You see 2 platform registration entries You see a single deployment for both registrations The details column for the 2 entries has the same issuer, but different client_id values. Copy the values of client_id and issuer for one of the entries and store them somewhere (doesn't matter which one) Click "Register a platform" Enter the values for issuer and client_id - the ones you just copied. Enter a name and 'http://example.com' for the other URL fields. Save the form Verify you see a form validation error on the "Client Id" field, stating that the value of the client_id has already been registered under this issuer Change the client_id to something else and save Verify the entry was saved successfully.