/summon magma_cube ~ ~1 ~ {Passengers:[{id:"minecraft:zombie"}]}
This one will do it. I simply pasted the command i was using while playing in creative, maybe I just copied it wrong. Anyway this one right here should work. Otherwise let me know what error gives to you or just summon a zombie on a magma cube
/summon magma_cube ~ ~1 ~ {Passengers:[{id:"minecraft:zombie"}]}
This one will do it. I simply pasted the command i was using while playing in creative, maybe I just copied it wrong. Anyway this one right here should work. Otherwise let me know what error gives to you or just summon a zombie on a magma cube