Don't receiving confirmation of the changes from the xbee

Projects Networking, Protocols, and Devices
2 
    if (Serial.available() > 1) {
   
      for (int i=0; i<3; i++) {
        incomingChar[i] = Serial.read();
      }

If there are 2 bytes, read all three of them. Hmmm... Fail!

      if ( strstr(incomingChar, okString) != NULL ) {

You can't pass a non-string to a string function. Fail!

A string is a NULL terminated array of chars. All you have is an array of chars, which is NOT a string.