Invalid response ".well-known"

My domain is: N/A

I ran this command: sudo certbot --nginx -d mysite.com -d www.mysite.com

It produced this output:
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator nginx, Installer nginx
Starting new HTTPS connection (1): acme-v02.api.letsencrypt.org
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for mysite.com
http-01 challenge for www.mysite.com
Using default address 80 for authentication.
Using default address 80 for authentication.
Waiting for verification…
Cleaning up challenges
Failed authorization procedure. mysite.com (http-01): urn:ietf:params:acme:error:unauthorized :: The client lacks sufficient authorization :: Invalid response from http://mysite.com/.well-known/acme-challenge/UH-geFrEdUN10Br3dAN4uoT0biA2sxXXrf80: "

Not Found

The requested URL /.well-known/acme-challenge/UH-geFrEdUN10Br3dAN4uoT0biA2sxXXrf80 was not found on ", www.mysite.com (http-01): urn:ietf:params:acme:error:unauthorized :: The client lacks sufficient authorization :: Invalid response from http://www.mysite.com/.well-known/acme-challenge/geFrEdUN10Br3dAN4uoT0biA2sxXXrf80: "

Not Found

The requested URL /.well-known/acme-challenge/geFrEdUN10Br3dAN4uoT0biA2sxXXrf80 was not found on "

IMPORTANT NOTES:

My web server is (include version):
ubuntu 16.04
nginx 1.10.3
certbot 0.28.0

The operating system my web server runs on is (include version):
as above

My hosting provider, if applicable, is: N/A

I can login to a root shell on my machine (yes or no, or I don’t know): Yes

I’m using a control panel to manage my site (no, or provide the name and version of the control panel): No

The version of my client is N/A