If Beoplay Portal are connected to a USB-C cable, disconnect, then reconnect the cable and try again.
If connected via Bluetooth, your Beoplay Portal have a Bluetooth range of up to 12 meters (in line of sight). However, Bluetooth connectivity might be affected by other active Bluetooth devices in the nearby area (e.g., mouse, keyboard, mobile phone, laptops, or 2.4 GHz routers). Try to keep the headphones away from other active Bluetooth devices.
If your Beoplay Portal are still unresponsive, find out how to reset them here.