If you install a RelaxedSIM data only SIM card in a Victron LTE modem (for example the Victron GX LTE / Cerbo GX setup) and the SIM seems to register but no data usage appears in your account, the cause is almost always the same: the APN was left empty. The modem’s data roaming is enabled by default and does not need to be changed. Set the APN to globaldata, save, reboot, and the data-only SIM starts working on the AT&T network.
Victron LTE modem + RelaxedSIM: the fix that worked
- Open the Victron GX modem / cellular settings on your device (Settings → Services → Modem or Cellular, depending on the firmware).
- Enter the APN:
globaldata. Leave the username and password blank. - Leave data roaming ON — Victron enables roaming by default, and this is correct for a prepaid data SIM card that connects through AT&T, T-Mobile, or Verizon.
- Save the settings and reboot the Victron unit.
- Wait a few minutes, then check the RelaxedSIM portal with the SIM’s ICCID. Data usage appears once traffic starts.
Why does the SIM show as working but no data usage syncs?
A modem can show a signal even when no APN is configured, because the SIM registers on the network but has no data path. In this support case the ICCID looked inactive in the portal until the customer entered globaldata. Once the APN was saved and the modem rebooted, the SIM connected on AT&T and usage began syncing. If you scan the ICCID barcode and still see no data, first confirm the APN is entered — not just the SIM inserted.
RelaxedSIM data only SIM cards for Victron remote monitoring
Victron owners use a data SIM card inside the LTE modem as a mobile hotspot SIM card for VRM remote monitoring, battery and solar telemetry, and firmware updates. Because the Victron modem works like an AT&T hotspot SIM card scenario, a data only SIM card for hotspot use is the right product — no calls, no SMS, just reliable data. Unlike SIM cards with prepaid minutes, RelaxedSIM is a data-only service, so there is no voice balance to manage. The customer in this support case used the 24GB/360-day IoT prepaid data SIM card, which is the best fit when a Victron installation runs year-round and continuously sends battery, solar, and inverter data to VRM.
RelaxedSIM also sells IoT SIM cards for routers, cameras, trackers, and marine or off-grid equipment. You can compare every option on the USA data SIM cards page, and see full settings on the RelaxedSIM APN details page.
Frequently Asked Questions
Does the Victron LTE modem need an APN for RelaxedSIM?
Yes. Enter APN globaldata with a blank username and password. Without the APN, the modem can register on the network but data does not flow.
Should I turn data roaming off or on in the Victron modem?
Keep it ON. Victron’s modem has roaming enabled by default, and a prepaid data SIM card needs it to connect on AT&T, T-Mobile, or Verizon.
Why does my ICCID show no data usage in the RelaxedSIM portal?
First make sure the APN is entered and the modem was rebooted after saving. Usage syncs once data actually passes through the SIM. If it still shows nothing, confirm the ICCID matches the card installed in the modem.
Which data SIM card should I use as a hotspot plan for Victron?
For a year-round Victron installation that continuously pushes data to VRM, choose the 24GB/360-day prepaid data SIM card — the plan used in this support case. For a seasonal site with lighter telemetry, the 6GB/90-day plan is a smaller option.
Does RelaxedSIM work with AT&T in the Victron modem?
Yes. In this support case the modem connected and passed data on the AT&T network after the APN was entered. RelaxedSIM data only SIM cards also connect on T-Mobile and Verizon as coverage allows.