How does certbot bind port? Could not bind TCP port 80 because it is already in use by another process on

I enabled both 80 and 443. sudo certbot certonly --standalone --agree-tos --no-eff-email --staple-ocsp --preferred-challenges http -m **@**.com -d mycomp.com Saving debug log to /var/log/letsencrypt/letsencrypt.log Requesting a certificate for mycomp.com - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Could not bind TCP port 80 because it is already in use by another process on this system (such as a web server). Please stop the program in question and then try again. Let's Debug shows ANotWorking ERROR mycomp.com has an A (IPv4) record (*.***.***.***) but a request to this address over port 80 did not succeed. Your web server must have at least one working IPv4 or IPv6 address. I do not understand what is wrong with port 80. How to fix this?