If a client sends a GET request, you call Toggle(), regardless of whether the request was an initial connection or a form submit request. Toggle() is a useless name, because that function does NOT toggle anything.
Why is the form open tag sent in Button() while the form close tag is sent in loop()? The entire form should be sent in the function.
Serial.print()ing the GET request would be a useful thing to do, as would showing us the output.