curl --request POST \
  --url https://app.autoposting.ai/api-proxy/billing/change-plan \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "planId": "plan_business"
}
'

{
  "success": true,
  "data": {
    "currentPlanId": "plan_pro",
    "pendingPlanId": "plan_business",
    "effectiveAt": "2024-02-01T00:00:00Z"
  }
}