Using command blocks to set players on fire

I want to use a command block to set a player (which already has permanent fire resistance) permanently on fire, mostly as an aesthetic. Right now I have the following command:

/data merge entity <Playername> {Fire:100}

When I run it it says "Unable to modify player data". How do I get this to work? I'm new to commands in Minecraft.

This approach could work:

/execute at @p run summon minecraft:small_fireball ~ ~3 ~ {direction:[0.0,-10.0,0.0]}

It targets a player and constantly summons a small fireball from a Fire Charge around them, which would set the player on fire. You could potentially modify this a bit to create a permanent "on fire" effect.

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