so this is second place where you are trying to solve the same problem and it is unrelated to the 3 years old topic. also we can hardly help you with your c# code here, so maybe lets continue in your old topic and focus on your javascript code. Gordon suggested to test your JS code by using something verified like nrfconnect android app where you can connect to Bangle and send data to characteristics and verify your JS code works as expected.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
so this is second place where you are trying to solve the same problem and it is unrelated to the 3 years old topic. also we can hardly help you with your c# code here, so maybe lets continue in your old topic and focus on your javascript code. Gordon suggested to test your JS code by using something verified like nrfconnect android app where you can connect to Bangle and send data to characteristics and verify your JS code works as expected.
If it works there then it is in your c# code.
Also if you are into c# you can also test with bleconsole https://github.com/fanoush/BLEConsole it can also read/write to characteristics. subscribing to nordic tx and writing to nordic rx example is here https://gist.github.com/fanoush/c17263e57e5ea204de7b2bb01d2a258f#file-bleconsole-log-L24