MCU to switch single coil latching relay not working (attempting array with common gnd)
You need to use an h-bridge as if you were driving a motor. For this kind of relay you need to be able to both sink and source current, which a Darlington pair cannot do, it can only sink.

I guess you may be being thrown by the symbol of an inverting buffer used in the schematic symbol for the ULN2803 in your schematic capture package. It's incorrect, since it's not an inverting buffer, it's a Darlington pair:







simulate this circuit &ndash; Schematic created using CircuitLab

As you can see, setting the input HIGH will allow the transistor pair to conduct, but setting it to LOW will stop it conducting - so the output is either connected to ground, or is floating.