I'll second dababy, please post pictures of what the wiring looks like now (and please make sure they are in focus!).
Let's go through this together. For right now, it might be best to bring this all down to the bare bones, and test from there. Disconnect everything between the USB-C PD Board and the PMS, with the exception of BTN and GND. Disconnect the fan for now as well. All that should be wired up to the PMS for bare functionality are B+, B-, BTN and GND.
From there, measure your battery voltage. If the batteries are below a certain threshold voltage (I believe it to be somewhere around 3.5 volts, but I'm not 100% positive), the PMS will either not turn on, or otherwise not function correctly. If your battery voltage looks good, press and hold the button on the USB-C PD board for 2 seconds. Measure for voltages on each of the voltage pads on the PMS. If everything looks good there, you can add the wires to the USB-C PD board back in.
Basically you just want to start with the bare bones, and slowly add each piece, testing between adding new parts.