Bring the POWERUP close to the smartphone. Pairing is done by proximity between phone and smart module, just "Touch & Go".
Open the app. The app will display "searching" until a connection is established.
When the connection is established the POWERUP LED will double blink, the app "searching" note will disappear and the battery level and dBm level will show.
Make sure that WiFi is turned off and Bluetooth is turned on.
For Android smartphones, check that "location" services are enabled
For iPhone with IOS 11 or newer, slide up the Control center and check that the Bluetooth is turned on. You might need to restart your phone if it doesn't connect.
If the app keeps showing "searching" and the module doesn't connect, restart the module, kill the app (force stop it) and launch it again.
Make sure no one else has already connected to your POWERUP. If the LED light blinks twice every second, it means it is already connected to another phone. Turn the module off and on again, move away from other phones, bring the POWERUP close to your's and try connecting again.