Web thermometers, monitoring systems, and PDUs from manufacturer Didactum equipped with a GSM or LTE modem can output error and status messages. The Didactum programmers have compiled the most important messages related to GSM and LTE modems for you here:

System message:	Cause:	Solution:
„+CMS ERROR: 500 (unknown error)“	1. The LTE / GSM modem is not registered in the mobile network. 2. Insufficient credit to send a message. 3. The network is overloaded and cannot send a message at the moment. 4. Incorrect service center number or phone number entered. 5. The antenna cable is not properly connected or is defective.	1. Check the signal level of the GSM / LTE modem in the web interface. 2. Check if the antenna is properly connected. 3. If signal quality is poor, please use a different antenna (e.g., weatherproof outdoor antenna). 4. Check if the SIM card has already been activated by the mobile provider. Test the SIM card with a smartphone if necessary. 5. Check if the PIN code used is correct. 6. Check if the service center / SMS center number has been entered correctly.
GSM modem: Found internal ‘modem’	The web thermometer / monitoring system / PDU is initializing the built-in modem.	1. Wait until the initialization of the GSM / LTE modem is complete (typical duration after start / restart approx. 15 seconds).
+CMS ERROR: (Unassigned (unallocated) number	The target (SMS) requested by the modem cannot be reached because the number has a valid format but is currently not assigned.	1. Check the entered phone number.
GSM modem: Error, check your SIM card and PIN code	No SIM card installed / incorrect PIN code entered.	1. Check if the SIM card is correctly inserted. 2. Clean the SIM card contacts if necessary. 3. Check the PIN code of your SIM card.
+CMS ERROR: 97 (Message type non-existent or not implemented)	Message type non-existent or not implemented	The message type to be sent is not supported by the monitoring system.
+CMS ERROR: 69 (Requested facility not implemented)	This usually indicates an error in the SMS center number.	1. Check if the SMS center number has been entered correctly in the monitoring system.
+CMS ERROR:29 (facility rejected)	The service requested by the modem is not supported by the mobile network.	1. Try using a different SIM card. 2. Use a previously tested SIM card. 3. Send an SMS command to the monitoring system. 4. Check if the SMS center number is correct.
LTE service: connection cannot be established	After 5 failed attempts, the system could not establish a connection to the specified APN.	1. Check the LTE settings in the monitoring system. 2. Check if LTE / 2G reception is available. 3. Update the firmware of your Didactum system.
+CMS-ERROR: 310	SIM card not inserted.	1. Check if the SIM card is correctly inserted into the 2G-GSM / 4G-LTE modem.
+CMS-ERROR: 515	Modem is currently in use or invalid character in the string.	1. Check if an OpenVPN connection is already active. 2. Restart the web thermometer / monitoring system / PDU if necessary.
+CMS-ERROR: 534	Cell broadcast error unknown	1. Please try a SIM card from another mobile provider. 2. Contact your mobile provider.
+CMS-ERROR: 316	SIM PUK required	1. Enter the PUK of your SIM card.