SSL from example.com

My website is running perfectly fine until today for some reason, SSL 30 days free from LetsEncrypt changed to Self-signed that will expire in 3649 days.
Because of this event, our chatbot created on Facebook app gets a warning that it no longer can send data to our webhooks.
Below are some messages that I can find on our log files.
and some screenshots (Untitled — ImgBB)
[03.19.2020_05-31-02] Trying to obtain SSL for: hoanghai.langtech.vn and: www.hoanghai.langtech.vn
[03.19.2020_05-31-02] /root/.acme.sh/acme.sh --issue -d hoanghai.langtech.vn -d www.hoanghai.langtech.vn --cert-file /etc/letsencrypt/live/hoanghai.langtech.vn/cert.pem --key-file /etc/letsencrypt/live/hoanghai.langtech.vn/privkey.pem --fullchain-file /etc/letsencrypt/live/hoanghai.langtech.vn/fullchain.pem -w /home/hoanghai.langtech.vn/public_html --force
[03.19.2020_05-31-15] Failed to obtain SSL for: hoanghai.langtech.vn and: www.hoanghai.langtech.vn
[03.19.2020_05-31-15] Trying to obtain SSL for: hoanghai.langtech.vn
[03.19.2020_05-31-18] Failed to obtain SSL, issuing self-signed SSL for: hoanghai.langtech.vn
[03.19.2020_05-31-18] Self signed SSL issued for hoanghai.langtech.vn.

Hey there. I have the same issue. But I think, it’s caused by the rate limit of let’s encrypt.
See this one: Rate Limits - Let's Encrypt

You can see the error from the terminal, try this (change with your own domain):
/root/.acme.sh/acme.sh --issue -d cyberpanel.xyz -d www.cyberpanel.xyz --cert-file /etc/letsencrypt/live/cyberpanel.xyz/cert.pem --key-file /etc/letsencrypt/live/cyberpanel.xyz/privkey.pem --fullchain-file /etc/letsencrypt/live/cyberpanel.xyz/fullchain.pem -w /home/cyberpanel.xyz/public_html --force