Lua Roblox HttpService:PostAsync Stripping Json - json

Question

I'm trying to validate against an external API that uses hashing against the body + API.
In Roblox I have:
body = '{"attributes":[{"name":"player_level","value":120},{"name":"is_whale","value":true,"data_type":"boolean"}]}'
Which I then call this:
local attributeData = game.HttpService:PostAsync(encoded_url,body,Enum.HttpContentType.ApplicationJson,false,headers)
But in my logs:
19 Aug 2022 20:44:34.8862022-08-19 20:44:34 +0000 severity=INFO, method=POST path=/api/v1/appuser/toms_awesome_rblx_guy1/attributes format=json controller=Api::V1::Appuser::AttributesController action=create status=0 duration=1.09 view=0.00 db=0.00 ip= attributes=[{"name"=>"player_level", "value"=>120}, {"name"=>"is_whale", "value"=>true, "data_type"=>"boolean"}] session_id=62f52645795301001985e2d7 enc=0fea853f09e361b9d80579d99acda0a69c8e3c7045a2834d30b03e650a5d5f86 appuser_external_id=toms_awesome_rblx_guy1
Notice how the {}'s were stripped off to become this: attributes=[{"name"=>"player_level", "value"=>120}, {"name"=>"is_whale", "value"=>true, "data_type"=>"boolean"}]
This is ultimately causing issues with validation because the hash was made on my end with the {}'s.
Any ideas where I'm going wrong? I've tried different combinations of Enum.HttpContentType.ApplicationUrlEncoded and "data="..body and encoded_body = game.HttpService:JSONEncode(body)
But they all seem to append things in front of the generated json in the logs like data= or _json=. None of which were in my original hash based on the body json string I wouldn't expect to change.