This product has TX (transmit) mode and RX (receive) mode. It is Bluetooth 5.4. TX mode is a mode that can be plugged into a 3.5mm jack on a computer, smartphone, TV, etc., and wirelessly transmit audio to earphones, etc. Supported codecs are AAC and SBC, the same supported codecs as iPhone. RX mode is a mode that connects the product to headphones or earphones, and can wirelessly send audio from a smartphone, computer, etc. The supported codec is SBC only. The instruction manual has been lost and is not included. Please refer to the following site for instructions. (We do not provide support for usage) https://manuals.plus/ja/ugreen/cm672-bluetooth-audio-receivertransmitter-manual