curl --request POST \
  --url https://api.iotools.cloud/v1/tool/function-composition-calculator \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "functionF": "x + 3",
  "functionG": "x - 3",
  "x": "5"
}
'

{
  "tool": "function-composition-calculator",
  "tool_version": "1.0.2",
  "outputs": {
    "fx": "8",
    "gx": "2",
    "fgx": "5",
    "gfx": "5",
    "steps": "f(x) = x + 3\ng(x) = x - 3\nx = 5\n\nf(5) = 8\ng(5) = 2\n\nf(g(x)) = f(2) = 5\ng(f(x)) = g(8) = 5"
  },
  "credits_used": 5,
  "credits_remaining": null
}