On DNS Multitenant Setup

bench config dns_multitenant on
bench setup nginx
sudo service nginx reload

Connect Custom Domain with site

bench setup add-domain [desired-domain]

Example: bench setup add-domain erp.aadhilpm.com

bench setup nginx
sudo service nginx reload

bench restart
sudo apt install snapd
sudo snap install core; sudo snap refresh core
sudo apt-get remove certbot
sudo snap install --classic certbot
sudo ln -s /snap/bin/certbot /usr/bin/certbot
sudo certbot --nginx

Then based on the option and question shown on the screen mention required details