35115: Scheduling does not support this timestamp

SendAt time must be between 300 seconds and 35 days (3024000 seconds) in the future, inclusive.

Scheduler currently doesn't support scheduling a message at a fixed time less than 5 minutes from now, or more than 35 days in the future.

Verify that the SendAt parameter is using "[YYYY]-[MM]-[DD]T[HH]:[MM]:[SS]Z" format (in UTC).