This usually happens only on iOS devices. When a http:// or https:// link is included at the end of a message, iOS will show the link as a preview first. The user then has to click a second time to go to the final URL. Quite annoying in most cases.
To get around this issue, either:
- remove http:// or https:// from the link, or
- add additional text after the link. If the http:// or http:// link is not at the very end of the message, iOS will not show it as a preview, but rather a clickable link.
Our friends at Tatango made a really helpful video explaining this: