No more candidates to test error on RP Zero 2 connected to the EINSY RAMBo on a Prusa i3 MK3S

What is the problem?

I connected a Raspberry Pi Zero 2 to the EINSY RAMBo of my Prusa i3 MK3S, following Prusa's guide exactly. Attempting to connect gives me the error: Offline after error
No more candidates to test, and no working port/baudrate combination detected.

I've been looking for solutions everywhere and it's just people saying they fixed it by trying a different USB cable. But this isn't powered by USB, it's via pins directly to the Prusa

What did you already try to solve it?
Changed the baudrate from auto to all the different values. Restarted Octoprint. Restarted the system. Restarted the printer. Made sure I had a good physical connection. RPi port is set to on.

Logs (syslog, dmesg, ... no logs, no support)

Changing monitoring state from "Offline" to "Detecting serial connection"
Performing autodetection with 0 port/baudrate candidates:
Changing monitoring state from "Detecting serial connection" to "Error"
Changing monitoring state from "Error" to "Offline after error"

Additional information about your network (Hardware you are trying to connect to, hardware you are trying to connect from, router, access point, used operating systems, ...)

You were looking at the wrong guide - your guide was for their deprecated prusaprint image.
What you need is a guide for Octopi images.

That guide is also a little outdated. Use dtoverlay=disable-bt instead of dtoverlay=pi3-miniuart-bt in /boot/config.txt.