Illustration from a solid state “relay” product
Power is going in at 'plus' and leaving at 'minus', at the “out” terminals of the Solid State Relay.
And here is a simplified schematic of the internals of a DC-DC SSR
Notice the diode inside the MOSFET symbol? It goes from - to +
The diode is a natural effect of the way a MOSFET is made, and not something that is put there as an extra ting.
So I would say, try again, but this time with power going from + to - on the SSR's
Sources: How_to_wire_SSR - Point 4.1
After thoughts:
Since we are trying to make +24V available to the “-” out of the SSR, then the SSR must internally have a High-Side driver chip, that triggers the MOSFET Gate, as Gate voltage must be some 10V-15 higher than the “-” out side of the mosfet (the Vgs voltage).
See also this image of a High-Side driver:
Most likely the SSR will have an internal High-Side driver chip included in its belly.
Sources2: Infineon.com High-Side drivers