I am having an odd issue. I have no issue recording guest voices onto the Zoom H4n Pro when I'm calling them using my cellphone or computer. But, when I use my Cisco landline phone, their voice is not being recorded from the landline to the H4n Pro. Why? What adapters do I need to do this successfully? Right now, I'm using a 3.5 mm aux cable that connects from the recorder to an RJ9 adapter that's connected into the landline. I'm using the same aux cable I use for my cell and computer.

When I upload the audio file, I can hear my voice (which is captured by a lavalier mic) only. But, when I'm on the landline phone with them, we can hear each other just fine. Despite this, their voice isn't being recorded onto the device. Why is it that when I'm using ONLY my landline, their voice is not being recorded?

Thank you!