certbot-auto is no longer available.
It still getting updates https://github.com/certbot/certbot/blob/master/certbot-auto
Forbidden</title>\n</head><body>\n<h1>Forbidden</h1>\n<p"
Try opening up your page in the browser to see what's going on. You might not setup your nginx/apache properly http://mydomain/.well-known/acme-challenge/i_fU1bFrQZzgfVI2FtWo8Ov0ITjplCcPj...