Stryd can only be paired with the phone from within the Stryd app. If you try to pair with Stryd from the Bluetooth settings from the phone operating system, Stryd will not pair. You might get a message like "Pairing Rejected by Stryd" (this is the message as reported by Samsung Android phone, other devices might report a slightly different message).
If you get that message, please open up the Stryd app on your phone and pair from the Settings menu.
If you need additional assistance, please contact firstname.lastname@example.org.