ODK collect - can't get blank form

1. What is the problem? Be very detailed.
I can't load a blank form, when I try the following message appears:
"Form list download failed
Collect can't reach the server at ..."
I can't access a form via qrcode either. I installed Central on DigitalOcean and made the SSL certification.


2. What app or server are you using and on what device and operating system? Include version numbers.

3. What you have you tried to fix the problem?

I made an ssl certificate.

4. What steps can we take to reproduce the problem?

5. Anything else we should know or have? If you have a test form or screenshots or logs, attach below.

Can you get to your Central website through the device's web browser?

To set up the device, did you follow the instructions in the documentation about Managing App Users?