It's possible that headphones or speakers may be automatically connected to another previously connected audio device, or the Bluetooth pairing isn't set correctly.
You may need to disconnect or unpair the connected mobile device to pair the headphones or speaker to the mobile device you want to use.
For LinkBuds (WF-L900): Make sure your Linkbuds have the latest software update using the Sony | Headphones Connect app. Downloads are posted on your model support page.
Check the Bluetooth® connections between the devices
If the headphones or speaker is connected with or paired to multiple devices, check the other device and disconnect the Bluetooth connection between that device and the headphones or speakers. Then try connecting with the desired audio device again. If you need assistance with disconnecting the Bluetooth connection on the other audio device, check the manuals for that device.
Pair (connect) using the Near Field Communication (NFC™) function
To make a Bluetooth connection using the NFC function, touch the smartphone on the N-Mark of the headphones or speaker. The smartphone terminates the BLUETOOTH connection with the current device and connects with the headphones or speaker. Keep touching the headphones with the smartphone until the smartphone reacts.
Pair (connect) using a Bluetooth connection
Separate articles are available to establish a Bluetooth connection between your smartphone and headphones or speaker.