Capturing audio from Safari with Audio Hijack Pro

Hi, I'm trying to use Audio Hijack Pro to capture some audio from Safari. Have not done this for ages and maybe it worked last time, can't remember for sure - but now it's saying to me Capturing audio from Safari requires the Instant On extra, which is not yet available for this system. I'm using a Macbook Pro from 2012, OS 10.11.6

Can anyone tell me what this message means? Any other way I can record some audio from Safari?