AirPort Express set-up for client mode
I'm having difficulty restoring AE to client mode, using "add to existing network" in the AE utility, version 638.9. I purchased the AE this year, and got it to stream iTunes music. A week ago the wifi modem was accidentally turned off for several hours. The modem was subsequently powered up successfully, but the AE would not auto-connect to the wifi (unlike my AppleTV). The AE's LED status has since been displaying a slow blink. The wifi signal throughout my small apartment is excellent. I also have no AE main base station. I've read the relevant support notes and guides; followed the client-mode set-up instructions, to no avail. I've reset the AE numerous times, also returned it to factory default, then attempted client set-up, again to no avail. Am I missing something? Any solutions? Here are some relevant screen shots, approximately in sequential order:
AirPort Express 802.11n (2nd generation), macOS High Sierra (10.13.5), Apple TV 2nd gen.