Flashing red stands for "Abnormal Status". These are a few things to look for to help:
1.Remove SD Card and reinsert, may need to be reformatted from the app as well
2.Remove Db2 from power and let the Db2 power down totally, then reconnect to power.
3. Check for firmware update.
a.https://support.nellyssecurity.com/hc/en-us/articles/360038885453-How-to-Upgrade-Your-NSC-DB2-Video-Doorbell-s-Firmware
You can always reach out to support as well ->
customerservice@nellyssecurity.com / 855-340-9999