Step 1 - Check if Onboarding is Enabled
As a security feature, your hotspot is discoverable for onboarding for the first 5 minutes after it boots up - this is indicated by the Onboarding LED, the 4th LED from the left.
After the 5 minutes are up, the hotspot will no longer be discoverable for Onboarding and the Onboarding Enabled LED will turn off.
You can power cycle your hotspot to make it discoverable for onboarding again.
Step 2 - Check your Network Configuration
Check your network configuration on your modem or router. If there are any settings like "don't allow communication between devices on the network", disable that setting and try onboarding again.