Please check that the email address you have entered is correct.
If the email is correct, it could be that our email was caught by recipient's Spam filter. We do everything we can to by-pass spam filters but sometimes unfortunately it happens anyway. If our emails are caught in a Spam filter, links will be automatically disabled by the email provider. In this case it is important to mark our emails as "Not Spam" if they find them there.
Another option to avoid our emails getting caught in a spam filter in the future is to add our email address email@example.com to address book, this way signifying that we are a trusted sender.
If the recipient could not find our email in their Spam folder, please ask them to check their "All Mail" folder. Most email providers have such an option. It could be that the email provider had allocated our emails into a different folder than Spam (such as Marketing or Promotional), and it is then easier to simply view "All mail" folder instead.