Force an error by modifying Moodle's code Open the file admin/tool/mobile/classes/external.php . Search this line: $settings = api::get_config($params ['section'] ); Add a new line right after that one with this code: $a = 1 % 0; Test the issue As admin, go to "Site administration > Development > Debugging" and set "Debug messages" to NONE. Create a new user (Site administration > Users > Accounts > Add a new user). Enable "Mobile services": Site administration ► Mobile app ► Mobile settings Create a Token in the mobile app service for the user created in step 2: Click on Site administration ► Plugins ► Web services ► Manage tokens Next, you can do a CURL REST call simulating a WS client with the user. You need to replace the WSTOKEN and the SITEURL of your moodle instance. curl 'http://SITEURL/webservice/rest/server.php?moodlewsrestformat=json' --data 'requests [0] [arguments] ={}&requests [0] [function] =core_webservice_get_site_info&requests [0] [settingfilter] =1&requests [0] [settingfileurl] =1&requests [1] [arguments] ={}&requests [1] [function] =tool_mobile_get_config&requests [1] [settingfilter] =1&requests [1] [settingfileurl] =1&wsfunction=tool_mobile_call_external_functions&wstoken=WSTOKEN' | python -m "json.tool" Confirm that after executing the request: You get a "responses" array. The first object in that array has ' "error": false' and a bunch of other data. The second object in that array has ' "error": true' and a "exception". Check that the exception does not have a  debuginfo or  backtrace property. As admin, go to "Site administration > Development > Debugging" and set "Debug messages" to DEVELOPER. Repeat step 5. Confirm that after executing the request: You get a "responses" array. The first object in that array has ' "error": false' and a bunch of other data. The second object in that array has ' "error": true' and a "exception". Check that the exception has a  debuginfo and  backtrace property.