DIAGNOSIS Full bars means it's connected to your router, but it can't reach Amazon's Alexa servers. This is an internet connectivity issue, not a local Wi-Fi issue.
FIX Reboot your entire network. Unplug your modem and router, wait 30 seconds, plug the modem back in, wait for all its lights to stabilize, then plug the router back in. Finally, restart the Echo Hub (mic off + volume down button). This clears the path from your device to the internet. Also, check if there's an Amazon Web Services outage—a quick web search for "Alexa down" will tell you.
IF THAT DIDN'T WORK The Hub's DNS settings might be stuck. On the Hub, go to Settings > Network, tap your Wi-Fi network, and forget it. Rejoin the network. This forces it to fetch fresh DNS info from your router. If your router allows custom DNS, try setting it to a public one like Google's (8.8.8.8) as a test.
HEADS UP This error often pops up after a router firmware update that changed firewall or security settings. If you recently updated your router, check its logs for blocked traffic to Amazon domains (like amazon.com, amazonaws.com). You may need to whitelist them.