To use a looper with an Amplifi 150, I came up with 2 different methods:
1. I ran a stereo cable from the headphone jack with a splitter on the end, sending one side to the looper pedal and the other straight, both into my PA system.
With this method you do not get to use of the speaker setup on your Amplifi.
2: ABY box between the guitar and the amp, and running the 2nd cable to a different amp with the looper in it. I could get the loop going on the 2nd amp, click the ABY button so it would sound like 2 guitars on 2 different amps.