Diagnosis
The vacuum's Wi-Fi module is not in pairing mode, or the 2.4GHz network requirements are not met.
How to Fix It
On the vacuum's screen, swipe to the settings menu (gear icon). Select 'Wi-Fi'. Ensure the Wi-Fi switch is toggled ON. The vacuum will display a network name starting with 'Tineco-'. On your phone, forget any previous Tineco network. Connect directly to this 'Tineco-' network, then open the app to complete setup.
If That Didn't Work
Your home router may be blocking the connection. Temporarily disable your router's 5GHz band and any 'smart connect' features. Ensure you are using a 2.4GHz Wi-Fi network with a simple password (no special characters).
Heads Up
The vacuum must be on the charging dock and powered on (screen active) for the entire initial pairing process. It cannot pair from a standby state.