curl --request POST \
  --url https://api.flashdocs.ai/v3/slides/{slide_id}/validate/text-placeholder-manual-insertion \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "text_placeholder_manual_insertions": [
    {
      "placeholder": "[title]",
      "value": "Introduce the topic of renewable energy and its importance."
    }
  ]
}'

{
  "all_valid": true,
  "validation_results": [
    {
      "placeholder": "[title]",
      "valid": true,
      "message": "The placeholder is too long. Currently 4 bullets, but needs to be less than or equal to 2 lines."
    }
  ]
}