Please make the test operation in the local server. Do not deactivate the plugin in the live site.
Please contact with us by using this contact form- http://wedevs.com/contact/. You have to select the question type as- “License activation problem”. We will solve your license issue as soon as possible.
I have tried to reproduce this issue but failed. It could be a has a chance of theme or plugin conflicts. You can disable all your plugins except Dokan and switch to a default theme of WordPress like – Twenty Twelve, Twenty Thirteen, Twenty Fourteen and let me know the results.