It seems that you have a device with a wrong modem module. It does not register to the operator at all.
Based on your device's product code (RUT24006XXXX), your device is made for Europe, the Middle East, Africa, Korea, Thailand, Malaysia regions. The LTE frequency bands, used by Flow (source), which are B2, B4 and B5, they are not supported by the modem module in your router. You can check RUT240 supported frequency bands here.