I'm trying to make a repeating command block that makes an arrow have an entity riding it when shot (I'm using a pig here as an example) but for some reason it says it modified the data but it isn't working. Can anyone help please?

my command:

data merge entity @e[limit=1,type=minecraft:arrow] {Passengers:[{id:pig}]}

I'm trying to make a repeating command block that makes an arrow have an entity riding it when shot (I'm using a pig here as an example) but for some reason it says it modified the data, but it isn't working. Can anyone help please?

My command:

data merge entity @e[limit=1,type=minecraft:arrow] {Passengers:[{id:pig}]}