There are more than 24 hours of calls in your call queue.
When you create calls via the REST API they are added to a call queue. Calls are removed from that call queue and placed at a default rate of 1 per second. This calls per second rate can be increased. Twilio will reject requests to place calls that will not be placed within 24 hours. At 1 call per second Twilio will reject calls once there are 86400 calls in your queue. More calls will not be accepted until your queue length decreases, calls in your queue will continue to be placed. If your application requires timely placement of calls, your application performance may be degraded.