@ZS1YT In both cases of router mode or AP mode the Deco SSIDs can be configured to be the same as your C80 SSID.

@Sethiest You should be able to do the connection in question as described in the TP-Link guide. You may also read through this guide and pay attention to the red notes for different scenarios.

@ZS1YT OneMesh and Deco mesh are different technologies and they don't work together. What you could do is to use your C80 as a main router and configure the Deco E4 in AP mode. Here's more info on...

@SUNITA123 Here's the official answer from TP-Link on your question.

@Arshad007 Have you tested to connect your computer directly to the POE switch and see if the issue is preset as well ? This way you could narrow down the issue to the EAPs configuration.

@mrunde Check this thread's solution to find answers on your questions.