I bought this one, pretty simple, just plug it into your handheld audio recorder, iPad or iPhone with the 3.5 jack adapter and it’s done. Zero trouble.

https://www.amazon.com/dp/B00HQMLFWC/ref=cm_sw_r_cp_api_i_nOmBCb14B5PER

Not a dumb question at all! I'm using this audio splitter (plug the male end into the plane's radio and my headset's respective plug into the female end. The USB-C plug goes directly into the GoPro and it records all audio that you hear in your headset (ATC, others people in your plane, and yourself).

That splitter is actually just a combination of these two items:

1. NFlightCam's Audio cable
2. GoPro Mic Adapter

So you could potentially purchase them separately for cheaper. Though the Nflightcam bundled cable does come with a little rubber thing that helps keep the two attached, though I can't say how helpful that really is, heh). Probably not worth the extra money that it costs.

I personally bought a this whole video kit that includes Nflightcam's GoPro splitter cable bundle, ND Filters, suction cup mount, battery door cover, and case.

I just use the voice memos app on my iPad.

Though it might be the cable. Try the NFlightCam one instead