My form cannot load in Enketo

We are working on installation and setu ODK Central in our local server ( Ubutu 16) following the instructions.

We have successfully installed and setup ODK central.
We can load the form in odk collect and send and receive data using odk collect app. However, we are not able to load the from on Enketo.

Hi there! When you get a chance, please introduce yourself here. I'd also encourage you to add a real picture as your avatar because it helps build community.

The error message suggests that there's something odd with your network config that is preventing Enketo from connecting to its local database. There are a lot of reasons why this could be, so you'll have to do some of your own troubleshooting.

Maybe you have a firewall up? Or are running other services on the server? Maybe it's Ubuntu 16 (we test with and recommend Ubuntu 18)?

Thanks for your reply. We will check our server configuration again and test it Ubuntu18. We let you know if it is working. Thanks