iOS Bluetooth LE: Code=6 “The connection has timed out unexpectedly.”:
https://stackoverflow.com/questions/32588325/ios-bluetooth-le-code-6-the-connection-has-timed-out-unexpectedly

Apple官方文件 – For establishing and holding a connection successfully:

Establishing your connection parameters for your accessory

Ref:
https://developer.apple.com/library/archive/qa/qa1931/_index.html