# Signal but no data troubleshooting checklist > Check activation, APN, allowance and device settings when your SIM shows signal but cannot send data. Setup & troubleshooting · 23 November 2025 If your device shows signal but cannot send data, check the SIM's activation, APN and remaining allowance first. Signal bars show only part of the connection. They do not confirm that the SIM has an active data service or that the device has the settings it needs. Work through the checks below in order. Change one thing at a time, repeat the same small test and record the result. This is more useful than repeatedly restarting the device or replacing an antenna before you know which part is failing. ## The ordered checklist 1. **Check activation.** Find the installed SIM in the ThingSIM portal and confirm that it is active. SIMs arrive inactive, so an unopened spare or a newly installed SIM needs activation before use. Match the device to the correct SIM record rather than relying on its position in a list. 2. **Check the APN.** Copy the APN shown against that SIM into the device's mobile data profile. Check spelling, spaces and the selected profile. A previous provider's saved settings may still be selected. Follow [setting the APN](/apn-settings) if you are unsure where the field belongs. 3. **Check the allowance.** Look at usage and whether the SIM has reached its allowance. ThingSIM pauses a SIM at its limit instead of charging overage. Move it to a larger plan straight away, paying only the difference for the rest of the month, or wait for the allowance reset. 4. **Check the plan.** Confirm that the plan matches where you are using the device and has enough allowance for its job. UK 3-network includes O2, Vodafone and Three; UK 4-network also includes EE. Europe roaming plans are priced per project, so do not assume a UK plan settles a European installation. 5. **Check network registration.** Read the device's mobile status page, not just its signal icon. Note any registration error and which network it reports. Follow the manufacturer's connection procedure and remove an old forced network selection if its instructions call for automatic selection. 6. **Check data roaming.** Inspect the device's roaming setting and follow its instructions for using a roaming SIM. A device setting that blocks roaming data can prevent the connection you are trying to make. Do not confuse enabling a device setting with buying coverage for a different country. 7. **Check the PIN prompt.** If the device reports that the SIM is locked or asks for a PIN, resolve that prompt using the correct supplied information. Do not guess repeated PINs. Record the exact message and ask for help if the required information is unclear. 8. **Check device bands.** Confirm the exact hardware model and its supported mobile bands with the manufacturer. A familiar product name is not enough when different versions exist. Ask whether that specific unit supports the networks and location you intend to use. ## Prove that the intended task works After each relevant correction, make a small test through mobile data. For a router, use a connected device and ensure another internet connection is not hiding the result. For a camera, send one image and check that it arrives. For a tracker, check that a new report appears rather than looking at an old position. If the device reaches its platform but a particular feature fails, record that distinction. A working upload and a failed remote viewing connection are different symptoms. Every ThingSIM gets a private IP at no charge, and that connection cannot accept unsolicited inbound traffic. Inbound access needs a [static public IP](/extras#static-public-ip) or private networking. A public IP is £8 a month per SIM and is directly reachable from the internet, so the customer must secure the device. Changing the APN is not a substitute for choosing the correct remote access arrangement. ## Separate settings from signal problems If the configuration checks pass, test the device in another practical position at the same site. Keep the settings unchanged while comparing results. Use [improving 4G signal](/improving-4g-signal) for a fixed installation, and test before committing to a permanent mounting point. For a router acting as a second connection, also check which connection the router is actually using. The [router failover sector page](/sectors/router-failover) describes that use case. A successful broadband test does not prove that the SIM works when broadband is unavailable. ## Record enough detail to get help Before using [contact](/contact), collect the SIM reference, device model, location, selected plan, saved APN and exact error message. Include what you tested and whether any data task succeeded. Avoid sending device passwords when a status message will explain the problem. UK 4-network 250 MB costs £1.20 per active SIM per month and is a useful starting allowance for modest connected equipment. Choose the final allowance from measured use, not from the strength of the signal icon. A failed card payment pauses new orders and plan changes, never SIMs already working in the field. ## Common questions ### Can I have signal after using all my data? A signal indicator does not prove that data service is available. Check portal usage because ThingSIM pauses the SIM when its allowance is reached. ### Will a larger plan fix an incorrect APN? No. Correct the APN separately; a larger allowance addresses usage limits rather than a device configuration error. ### Does a failed card payment switch off my working SIM? No. A failed payment pauses new orders and plan changes, never SIMs already working in the field. ## Recommended plan 250 MB, UK 4-network: £1.20 a month per active SIM, ex VAT. Source: https://thingsim.com/sim-signal-but-no-data