Some users tend to disable SSL for their domain, there is no simple way for enabling it for a user unless you edit the user file via terminal. Run this code to enable server wide.
cd /usr/local/directadmin/data
perl -pi -e 's/^ssl=OFF/ssl=ON/' users/*/user.conf
perl -pi -e 's/^ssl=OFF/ssl=ON/' users/*/domains/*.conf
perl -pi -e 's/^ssl=OFF/ssl=ON/' users/*/reseller.conf
perl -pi -e 's/^ssl=OFF/ssl=ON/' admin/packages/*.pkg
perl -pi -e 's/^ssl=OFF/ssl=ON/' users/*/packages/*.pkg