probably, you are entering the url for the destination system.
There is a known error in the plugin that prevents you from entering even valid data.
try this:
change line 76 of sfwd-lms-course-migration-admin from
var $url = $(‘#ldcm_receiver_url’).attr(‘value’) + ldcm_urls.endpoint;
to
var $url = $(‘#ldcm_receiver_url’).val() + ldcm_urls.endpoint;
That worked for me.
Regards
Uli