I can’t connect to the amplifier
Check that you are within bluetooth range.
Check that the amplier has power, at the least the standby LED should be on.
Check that you are using a compatible browser, ideally Chrome, Edge or Bluefy for iOS devices.
Check that your devices supports BLE (Bluetooth Low Energy) connections 

I can connect but my changes are not stored
Check that you have clicked save and reboot
If you have changed the bluetooth name you may have to “forget this device” then pair again