If your Smart Vent's LED is flashing red, it's likely not getting enough power to operate its louvers. There could be a few causes for this, but a good place to start is this video:
Additionally, the duct could be too snug of a fit for the vent, applying too much pressure on the vent's motor. If you feel comfortable doing so, you can use a hammer to try to widen the inside of the duct in the spot that's too-tightly impinging on the vent.
Lastly, try removing the vent from its duct and setting it on a flat surface. If it's still displaying a red LED and having trouble operating freely, please contact support for further assistance.