@Stephe1n Many thanks, I appreciate your response. @Kevin_Z Your answer solved the problem and now I have wifi throught out my apartment. Many thanks! The only thing I would add to the tutorial is...

@Kevin_Z Hello, Kevin_Z Many thanks for such swift response. All lights are solid blue. I was sitting right below the main router . The Cisco model is AIR-SAP1602I-A-K9...

The extender is unable to extended WiFi from Cisco router. I also have another TP-link extended connected to the same router (AC2600 aka RE650). Once I connect to RE450, it sees available Wi-FI...