There are actually two different types of Bluetooth technology.
1. BLE (or Bluetooth Low Energy) and
2. Bluetooth Classic (for Audio streaming)
The Jamstack 2 supports both, but they do work slightly differently.
BLE is used by the control app (it's also used in fitness wearables, smart locks, wireless keyboards etc).
BLE has several benefits. It's fast (for small amounts of data) and also it takes very little battery power.
This means, there is no need to enter a pairing mode on the device in order for it to advertise itself to the world (and thus connect to your amplifier). Simply go to the hardware tab on the control app, and hit connect.
Bluetooth Classic is different. This is the higher bandwidth (but higher latency) connection we all use all the time for streaming music to our Bluetooth speakers, cars, headphones etc.
Devices (like speakers) usually only have the ability to pair for the fist time during specific periods of time. Usually when the device is first turned on, or if a pairing mode is initiated by the user.
To enter BT Classic pairing mode on the Jamstack 2, simply double click (quickly) the first knob. You will see a swirling blue animation signifying it is looking for devices (like your smart phone).
Then (on your phone for example), navigate to the Bluetooth settings and you should see "Jamstack 2" as a device you can now connect to. Note you may also already be connected to BLE and you will see that there also, usually with a different symbol beside it (depending on the device).
With Bluetooth classic and the chip that we have, you can actually pair up to 5 devices at the same time. To do this, click three times (quickly) on knob #1 and repeat.
Once you've paired once, the Jamstack 2 will remember your device. This means, when you turn on your amp, and you're nearby, it will connect automatically. No action needs to be taken. If your phone's BT was off or not nearby and you want to "Link Back" to that previously paired device, you can double click knob #1 and it will look for familiar devices (only). To add new devices moving forward, use the triple click gesture.
If you want to reconnect a device previously paired, you do not need to enter pairing mode again, simply go to Bluetooth settings, and click "Jamstack 2" on your familiar devices list.
I hope that helps you navigate the world of Bluetooth!