Subscribe/unsubscribe from channels

flutter/lib/api/api_exception.dart

@@ -1,7 +1,7 @@
 class APIException implements Exception {
   final int httpStatus;
   final int error;
-  final String errHighlight;
+  final int errHighlight;
   final String message;
 
   APIException(this.httpStatus, this.error, this.errHighlight, this.message);