35114: Scheduling does not support this timestamp

This error occurs when the SendAt value for a scheduled message is outside the supported scheduling window or is not accepted as a valid timestamp. Use an ISO 8601 UTC timestamp, and make sure Twilio receives the request between 15 minutes and 35 days before the scheduled send time.

• The SendAt value is less than 15 minutes in the future when Twilio receives the request.
• The SendAt value is more than 35 days in the future.
• The SendAt value is not formatted as a valid ISO 8601 UTC timestamp such as 2026-05-15T14:30:00Z.
• Your application calculates SendAt too close to the minimum scheduling window, and the request reaches Twilio after that minimum has passed.
• Your application converts the scheduled time incorrectly because of a time zone or UTC formatting issue.

• Format SendAt as an ISO 8601 timestamp in UTC using the pattern YYYY-MM-DDTHH:MM:SSZ.
• Update the scheduled time so Twilio receives the request at least 15 minutes before SendAt.
• Update the scheduled time so SendAt is no more than 35 days in the future.
• Add a buffer beyond the minimum window if you are scheduling close to the earliest supported time.
• Generate and validate the timestamp in UTC before you send the API request.

• Message Scheduling
• Message resource API reference
• Messaging Services