Help with Steering Wheel Controls

Hey folks! I installed an Atoto S8 Premium in my 2013 Prius over the weekend, which mostly went well. It took forever to find the right wiring diagram to identify the SWC wires. I hooked them up and the head unit will recognize that I pushed a button, but it can't seem to differentiate *which* button I pushed. The right side controls for climate, trip, and display don't work either.

I've spent *hours* searching and can't seem to find any really solid information.

I imagine a resistor might be needed, but I can't find anyone referencing that except in Gen 2 Prius forums. I found a forum thread where someone claimed to have gotten their controls to work without using an Axxess AWSC-1 or similar, but then they ran into issues. Is the AWSC-1 a required component? Do I need some sort of canbus decoder?

I thought I might get this guy, but if that's all I need then tapping those wires should already be working for me...

Will this solve my issues? https://www.ebay.com/itm/295099149858

I'm thinking that the extra parts might not be the problem - since the controls for climate/trip/display don't work either, I'm thinking perhaps something has gone wrong that is preventing communication all around... unless that 28-pin connector somehow usually gets looped back around when you're plugged into the factory radio...

Any help would be greatly appreciated.

Since it took so long to find the wiring diagram, here's a bit for those who might stumble on this via Google in the future:
I'm driving a 2013 Prius with nav unit, non-JBL. I found the SWC wires on the 28-pin connector in pins 21, 22, and 23. They're red, green, and pink. I've attached the wiring diagram I found.

 

Update: After this post, I made sure that the ground for my SWC (the pink wire) was well connected, and I pulled the negative battery terminal in the trunk for a few seconds. After that, the right-side controls for climate control, etc started working again. Still no joy on the left side. To clarify my previous post - at one point I was briefly able to get the head unit to recognize that a button was being was pressed, but the signal was identical for each one. The HU couldn't differentiate between them. Most of the time, I got no response at all from the HU.

I ordered an AWSC-1 in hopes that would do the trick. A few days pass. While waiting for that to come in, I eventually installed the Atoto backup camera. Out of the blue, my head unit suddenly started recognizing the left-side SWC button presses! I ran through the configuration and it's been working great ever since.

So...... no idea. If anyone find this post via a Google search in the future, just know that 21, 22, and 23 *are* the right wires on the 28-pin connector, and you don't need any other sort of expensive adapters unless you have a JBL system. Make sure you have connected the SWC ground to the same ground as the HU, and pull the negative 12v battery terminal in the trunk before giving up.