Both IP's work! As you can see at the top of the forums, it says "play.manacube.com" but either IP should still connect you with no issues.
This is a really strange issue, however! - what happens when you do /usepack manacube? does an error pop up in chat? If you're still having issues, I could possibly send you the file for the texturepack, and you can manually apply it to your "serverresourcepacks" in your .minecraft folder. I can happily walk you through this if you're unsure!