You don’t need an active sub (I’ve been unsubbed since late Dec.). You need to reach rank 3 on the Trust Level system, thusly:
Alternatively, you can post a link by putting ` at the beginning and end of the link (or highlighting it, and picking the option at the top of the text box to the right of quoting), which embeds it like so:
https://wow.gamepedia.com/Hajiri
Though, this won’t show site previews, or images. Some trusted sites, like youtube, you can post anyway if you’re… rank 2, I believe.