@Mm10,

So flashing green means that it is searching for Wi-Fi 

To be sure, did you perform a factory reset(10 sec press of RESET) or a soft reset (5sec press of RESET)?

After resetting, you may consider removing the device from your Kasa app. 

At what point in the setup did you fail? Is your phone successfully connecting to the setup network broadcast by your switch for config?

Have you recently made any changes to your network? Do you have a guest or IoT network that you could try to connect the device to?

  @Mm10,

Hmm.

First, check to make sure that you have not set an IP reservation for the device in your router interface, and that your firewall is not blocking the connections. If you had set a custom name for the switch in the past, a reservation may have been created for you by accident.

What router are you attempting to connect the device to?

It could be possible that your modem or router was updated and turned on a feature causing the disconnect, such as Turbo-QAM. I have seen similar problems with Linksys updates in the past.

Also,  ensure that you do not have a VPN enabled and that you do not have Private Addressing enabled on your phone for your home network or the setup network.

Do you have another phone or tablet that you would be able to try and use to install the app?

If possible, I would highly recommend seeing if your router supports a guest network, as this may provide a bit more insight into where the issue lies.