What could cause a PD (access point) to not detect / pull power from a PSE (switch)?
Solution 1:
from port 1 on the PSE to the 24v PoE IN port on the PD
There's the problem. Apparently, the Aircube ISP uses a proprietary "PoE" variant as indicated by the 24V designation. IEEE PoE is 54/48V generally.
Ubiquiti is notorious for using various "PoE" variants. If they don't say 802.3af, 802.3at, 802.3bt anywhere, it's likely not compatible with any other vendor's device.
The PoE from the switch isn't of any use here, sadly. You'll need to put a compatible Ubiquiti 24V injector between switch and the Aircube.