Apologies for not seeing your post earlier, Paul1763.
I've already answered it on the other thread anyway (as other have done above) but, just for clarity, it's the FULL web address (INCLUDING the 'http' bit) that you need to include.
With most (possibly all?) browsers on a Windows PC, right-clicking in the address field for the relevant website will automatically copy the FULL address (even though the 'http' bit isn't actually displayed in the address bar) but it's possible that it might be different on other devices (such as an Android tablet or an iPad).
The link won't turn red until after you've clicked 'Submit'.
If you put something directly in front of 'http' (like the quote mark I've just used), AB's server won't spot it as a link. (Compare that with OG's post at 0720, where AB's server has tried to create a link even when there isn't one!).
If you put anything directly after a link (such as a full stop), AB's server will think that what you've added is still part of the link, thus invalidating it.
So it's best to give the link a line on its own (as 1ozzy did at 0627).