Many SMS problems on a Simbase SIM are not faults. They are cases where the SIM profile does not support what is being attempted. Check the table below first, because it often explains the problem before any troubleshooting is needed.

What your SIM profile can do

Expected behavior, not faults

My 89445 SIM sent an SMS and it never arrived

This is expected behavior, not a fault. On Blue, Yellow and Cyan profiles, every message a SIM sends is captured and posted in the Simbase platform, whatever number it was addressed to. It is not forwarded to that number.

So a device configured to text a technician's mobile will appear to send successfully, and the technician will never receive anything. The message is not lost, it is in the dashboard against that SIM.

If you need device messages delivered to an external phone, the options are to read them from the platform and forward them yourself, using Webhooks to trigger on the incoming message, or to use a Black, Red or Green SIM with the MSISDN add-on.

I can't text my Black, Red or Green SIM from my phone

Also expected. Without the MSISDN add-on, these SIMs have no phone number, so there is nothing for an external network to deliver to. They exchange messages only with the Simbase platform, which appears on the device as the +55555 shortcode.

Send to the SIM from the dashboard or the API instead. See SMS.

Which direction is failing?

Messages to the SIM and messages from it fail for different reasons, so establish which one you have before troubleshooting.

Messages to the SIM (MT)

Three cases, each with a different fix.

The SIM never receives the message

Start with whether the SIM is attached. A SIM that is not registered cannot receive anything, and a message sent to an offline device should not be assumed to arrive later. Confirm the SIM is enabled and registered, then send again. See Connectivity issues.

If the SIM is attached and messages still do not arrive, check whether it is registered on the circuit-switched side of the network. Incoming messages are delivered through there, so a device attached for data only cannot receive them, even though its data connection works perfectly.

You can see this in Diagnostics → Events. If the SIM shows GPRS location updates but no Voice location updates, it has not registered on the circuit-switched side.

The fix is on the device, and the exact setting differs by manufacturer. Look for:

• A network mode or service domain setting restricted to data only, and change it to allow both

• The manufacturer's documentation for SMS support, since some modules need SMS enabled explicitly

If you have AT command access, AT+CREG? reports circuit-switched registration and AT+CEREG? reports the LTE side, which confirms the same thing directly from the modem.

The SIM receives the message but does not respond

The message arrived, so the network path is working. What happens next is entirely down to the device firmware and the application running on it, which is outside what Simbase can see or influence.

Check whether the device is configured to reply to SMS and to execute SMS commands at all. On many routers this is a setting that is off by default, so the modem receives the message and nothing acts on it.

Then check the command itself. Most devices accept one exact syntax, and a command with the wrong keyword, spacing or password is ignored without any error. Compare what you sent against the device's own documentation, character for character.

A modem whose message storage is full will also stop accepting new messages, so clearing stored messages is worth trying.

The SIM receives the message and replies, but the reply never arrives

Messages to the SIM are working. The failure is on the way back, so troubleshoot it as an MO problem below.

Messages from the SIM (MO)

On Blue, Yellow and Cyan profiles, first rule out expected behavior: a message addressed to an external number is captured in the platform rather than delivered.

If a message the device sent is not appearing in the platform at all, this usually needs investigating on the network side. Contact support with the details below rather than continuing to change device settings.

If an external number can't reach your SIM

Blue, Yellow and Cyan SIMs are assigned one of two kinds of number, and they do not behave the same way. Check which one your SIM has in the dashboard before troubleshooting.

The +88 range is reserved for IoT devices. Not every mobile operator can route messages to it, so a message that never arrives may have been dropped by the sender's own network before it ever reached Simbase.

If your SIM has a +88 number and external messages are not arriving:

1. Send a test message from a different carrier

2. If it arrives from one network but not another, the sending carrier is the cause, not the SIM

3. If nothing arrives from any network, contact support

Still not working

Contact support with:

• The SIM's ICCID

• The direction that fails, to the SIM or from it

• The device make and model

• Device or modem logs covering the attempt

• The exact message or command sent, and the number or shortcode it was addressed to

• The approximate time the message was sent

• Whether any message has ever worked on this SIM

Common questions

Related

• SMS, sending and receiving from the dashboard and API

• SIM profiles, what each profile supports

• Webhooks, get notified when a SIM sends a message

• Connectivity issues, if the SIM isn't attached at all

• SIM state, enabling and disabling SIMs