Hello. I am having the same problem, but I'm very new to this and do not understand what is being recommended for the solution. I've attempted to use self signed SSL, which worked a bit, however the client devices are not being able to download forms that are published in Central and Enketo keeps loading until it gives an error. If I try using letsencrypt then central is not working, and the nginx is stuck at restarting. Can you please assist!!!
Some options you could consider:
Need it fast? Hosted by getodk with a free demo to start with.
Need it to just work? Follow the official set up without customisations.
Need a custom setup? You'll need a good understanding of the technologies and what happens at the points you're customising. (Been there, have my fair share of bruises)
Still stuck with a problem new to the forum? New post in support.
Good luck, let us know how you go!