I've handled many calls from users who experience this. The problem is almost always that they are using a single probe and trying to raise the mA's on a side with no probe plugged in. Each set of +/- keys will only control the probe or electrode patches plugged into THAT side of the toner. If nothing is plugged into that side then the toner will sense that there isn't a probe attached and will stop at 10 mA's. When using a single probe, you will only need to adjust the mA's using the +/- keys on the side that the probe is plugged into. That set of keys controls current to the entire probe.
If you are using two probes or a probe and a set of electrode patches and you are experiencing this issue then you should first check that the wires are fully seated in the water-proof sleeves at the end of each long wire. If there is a gap between the probe wire and long wire then the toner will not be able to sense that a probe is attached. Press together firmly. Add more water-based lubricant and insert your probes fully before adjusting the mA's. Your toner must sense your probe, sense adequate moisture, and sense full contact with skin before it will ungate and allow the mA's to be raised above 10.
If you are still experiencing an issue after following these troubleshooting steps then you can always reach out to the customer care team for support. Your toner is covered for a full year against manufacturing defect and customer support is available for the life of your product.