There are many reasons to get a certificate.
Two primary reasons that come to mind are when:
You intend on providing services securely.
You want to use a certificate as an authentication method.
But to answer your question directly - I would say NO, there is no requirement, that I know of, that would have you need to get a certificate.
It is merely a conscious choice, a decision you make for whatever reason(s) you may have.
Do you understand the difference between secure communications and insecure communications?
I think you have had a couple of good responses however your question is flawed
A) It’s not about the servers only its about the browsers as well. Most browsers are now preferring HTTPS communications from valid certificate authorities.
B) Have you had issues that you are not sharing that is leading you to evaluate installing HTTPS servirces?
Generally people on this forum are knowledgeable and helpful however you as a question asked need to do your bit as well and articulate what you mean instead of asking broad questions.
The application I have put on the server is OwnCloud. I have run it for a number of years and have had quite a few problems. The last problem was started when I did an upgrade and it crashed.
Finally, had to do a clean install.
Had the problem with it giving errors about SSL so I wrote the Mail on the Let’s Encrypt website. When I got back to the server the issue had changed to php not working.
At this point I am working on squashing the problems as they shows themselves.
I do appreciate the quick reply to my query on your site.
"I tremble for my country when I reflect that God is just; that his justice cannot sleep forever."
I have searched the web for a way to do that and have found nothing.
This is the reason I am trying to do all these things. I thought that
computers would be my companion as I grew older. But have found with the
modernization(?) of interfaces, auto spell, and the internet and its
security. I am not able do things the way I did.
Consequently, I am trying to simplify everything.
Thanks for any help you can offer.
I’m sorry you’re having trouble with this. There is presumably somewhere in your setup where a redirection from HTTP to HTTPS is happening. This could be in a configuration file for Apache, or it could be part of OwnCloud. If you can get rid of that redirection, you should be able to access the site in your browser with HTTP.