Are you trying to use the “link” button above the reply window? If so, it won’t work that way. Just directly paste the URL into the message itself, and it will be seen in the post. The “link” button only works when you’ve highlighted something, the clicked the “link” button, and pasted the link into the link window that appears in the process. Then when posted, the portion of your text that’s highlighted will become a link, even though the linked URL itself won’t show up in the actual message you posted (it will show in your browser, however, if you “mouse over” the text that you converted into a link as described above).
If that isn’t the problem, disregard – just hoping it would, and we could at least evaluate the links.