Moodle custom service creation issue

I am trying to create Moodle custom service for my functionality enhancement 1 ) https://docs.moodle.org/dev/External_functions_API 2 ) https://docs.moodle.org/dev/Adding_a_web_service_to_a_plugin updated service module based on these documents.created service module and external_lib.php file. But i got error while accessing the web service API Error : {"exception":"dml_missing_record_exception","errorcode":"invalidrecord","message" :"Can not find data record in database table external_functions."} Enabled debug mode and tried again . It shows external function registration error . {"exception":"dml_missing_record_exception","errorcode":"invalidrecord","mess age" :"Can not find data record in database table external_functions.","debuginfo":"SELECT * FROM {external_functions } WHERE name = ?\n[array (\n 0 => 'local_enroll_course',\n)]"} How can i register newly created service inside Moodle ? Pls Help