Short answer

Make sure the domain (and www) point at your hosting, then issue or renew the certificate in the Website Panel under SSL. If the padlock is still missing, the page is loading an image or script over http.

Why it happens

  • New site or moved domain: the free certificate can only be issued once the domain points at your hosting.
  • www missing: the certificate must cover both example.co.uk and www.example.co.uk.
  • Mixed content: the page is secure but includes something over http. In WordPress, set both addresses in Settings to https.