Sometimes VelongVPN will be blocked by the chinese government. When this happens, you'll need to reinstall your DuckVPN Profile. Start by opening the VelongVPN/OpenVPN Connect app. Then, click the edit sign next to the on off switch. You should see a delete profile button in the bottom left corner, click it.

After deleting the old profile, you should see an import profile page which prompts you for a URL. Enter velong.duck.enterprises as the url, and press next. If anything pops up press accept. You should now see a sign in page, enter your username and password. 

IMPORTANT: Make sure to check "Import Autologin Profile" before importing.