How to change config of a trial spawner?

Hello, I'm trying to create trial spawner configs that I can reuse across my adventure map to control what enemies are spawned, their names, equipment, potential drops, but having problem with setting them inside trial spawners blocks. I've created a simple data pack with file mypack:trial_chamber/prolog/weak_melee/normal.json with following contents
{
  "spawn_range": 10,
  "total_mobs": 6,
  "total_mobs_added_per_player": 1,
  "simultaneous_mobs": 2,
  "simultaneous_mobs_added_per_player": 0.5,
  "spawn_potentials": [
    {
      "data": {
        "entity": {
          "id": "minecraft:drowned",
          "CustomName": "Rotten Monstrosity",
          "CustomNameVisible": true,
          "Health": 10
        }
      },
      "weight": 1
    }
  ],
  "ticks_between_spawn": 100 
}

datapack is listed as enabled when used /datapack list command, then I stand on top of the trial spawner and execute following command /data merge block ~ ~-1 ~ {normal_config:"mypack:trial_chamber/prolog/weak_melee/normal"} but it isn't set in the block data, F3+I or /data get block ~ ~-1 ~ doesn't show any change, in the log I can see following error:
[13Sep2025 12:29:15.351] [Server thread/WARN] [net.minecraft.server.commands.data.BlockDataAccessor/]: [net.minecraft.server.commands.data.BlockDataAccessor] Serialization errors:
minecraft:trial_spawner // net.minecraft.world.level.block.entity.TrialSpawnerBlockEntity@BlockPos{x=-5, y=10, z=-34}: Failed to decode from map: Failed to get element ResourceKey[minecraft:trial_spawner / mypack:trial_chamber/prolog/weak_melee/normal]

if I use minecraft:trial_chamber/slow_ranged/poison_skeleton/normal as normal_config it's being set just fine, either I'm missing something or I'm trying to do impossible? I'm on 1.21.8 so trial spawner configs should be available, and I would like to use them as setting spawn potentials array with what I want is a quite lengthy command which does not fit into chat textbox at all.