ring pro keep flashing white during setup

Got a doorbell pro and having problem setting up. My existing doorbell is BROAN model 950W, which is in the compatibility list. First I installed the pro power kit (connected "transformer" and "front" terminals), then get rid of existing doorbell from the wall and connected Ring doorbell pro. Once power up, the light at the top of the circle is keep flashing. According to the installation note, ring pro needs time to prepare for setup and may take up an hour. I've waited more than one and half hour, the circle keep flashing, and it doesn't continue around the circle, only the top portion of the circle is flashing. Anyone can help what else I can do to finish the setup? Thanks!