curl --location --request POST 'https://api.conexteo.com/messages/sms/file?resumeBefore=true' \
--header 'X-APP-ID: <api-key>' \
--header 'X-API-KEY: <api-key>' \
--form 'external_id="123456789-client"' \
--form 'scheduleAt=""' \
--form 'shorturl=""' \
--form 'content="Hello World"' \
--form 'sender="SENDER"' \
--form 'file=@""'
{
"success": true,
"message": "message created",
"message_id": 123456,
"credits_used": 1
}