Airpods is unable to connect to Avantree Transmitter, Why?

Hi, I tried to connect my Airpods Avantree Transmitter Oasis B but failed. Is there anyone who had such kind of issue before and help?

Airpods are designed to be connected to one device at a time. So please make sure all previously paired with Airpods devices are Bluetooth-OFF when you try to use with Avantree Transmitter.
If Airpods do not reconnect to your Avantree transmitter, you may click the “CONNECT” button once to reconnect to it. Please note that it will be working well if transmitter shows CONNECTED and SBC lit up.