The AIU cable comes with the AIU, not the TIU. You need an RJ12 6P6C *reversed* (or some other word that means not straight) cable.
I bought following from Amazon and it worked.
InstallerParts RJ12 Modular Telephone Cord Extension- Reverse Wiring, Silver (14FT) https://www.amazon.com/dp/B01D...cp_tai_csgvEb5EWKVN6
Good luck,
Scott