Cannot connect to echo with my Apple wifi

I am not surprised.. they are different standards.

Amazon.com: Customer Questions & Answers

Amazon echo is designed to work with the Amazon Alexa .. and unless Amazon has made the echo airplay compatible or you use some other standard over apple network it won't work.

One answer there says airfoil worked but the sound was poor.. that is what is expected.. you are trying to mate chickens with ducks.

I have 5 Amazon Dots and 1 Amazon Echo, connected to 3 AirPort devices in my home (1 AirPort TimeCapsule and 2 AirPort Expresses). Four of the Dots are connected to 2 different AirPort Expresses. I have had NO ISSUES with connectivity, operation, or performance issues at all. Note that AirPlay is NOT used between the Echo devices and an AirPort. The Amazon devices utilize "Dual-band Wi-Fi 802.11 a/b/g/n (2.4 and 5 GHz) networks"--just as the AirPort Expresses do. So there should be no WiFi compatibility issues. The Alexa App walks you through the setup of your devices, and should automatically share the AirPort Express's credentials with the Amazon devices. Perhaps reset the Echo and try again with the Alexa App to enable connectivity. Hope this works for you.