Tandem handles issues with the connection between your Dexcom transmitter and t:slim X2 pump, questions about calibration, the “---” display, and sensor failures after the 2-hour warmup period.
For all other CGM issues, including sensor failures during the 2-hour warmup, “no restarts” alert, or physical problems with your sensor or transmitter, such as bleeding, bruising, skin reaction, adhesive issues, applicator issues, or broken wires, you should contact Dexcom using one of the options at https://www.dexcom.com/en-CA/contact-us-direct.