Can't get Lets Encrypt Certificate

Server Administration
1

I’ve been trying to get a Lets Encrypt certificate. Port 80 is open and I can access my simple-help server through port 80.

Everytime I click on “Generate your certificate”, I see that something is happening, then I can just press close, and I don’t get a certificate.

Here is what I found in the log

java.lang.Exception: WTOK not found for ref -7053048085792591917

Any solutions?