We are currently seeing some issues with the SMS service of TDC Denmark.
The traffic will be closely monitored whilst we expect an update and for the service to be functioning as intended again.
If you are sending critical messages we recommend that you use the Premium class until the disturbance is resolved. You can read more about the difference between our Standard and Premium class here: https://gatewayapi.com/standard-premium-sms/
Thank you for your understanding and we apologize for the inconvenience caused by this.