title: Getting com.android.volley.ServerError using the Volley library. What are some possible causes?
body: <p>When I make a request in Volley, I'm receiving <code>com.android.volley.ServerError</code> and response code 400.</p>
  <p>I'm doing something like this (generic example code):</p>
  <pre class="lang-java prettyprint-override"><code>final String param1 = &quot;...&quot;;
  final String param2 = &quot;...&quot;;
  // etc. 
  
  StringRequest stringRequest = new StringRequest(Request.Method.POST, API_URL,
          new Response.Listener&lt;String&gt;() {
              @Override
              public void onResponse(String response) {
                  Toast.makeText(MainActivity.this,response,Toast.LENGTH_LONG).show();
              }
          },
          new Response.ErrorListener() {
              @Override
              public void onErrorResponse(VolleyError error) {
                  Toast.makeText(MainActivity.this,error.toString(),Toast.LENGTH_LONG).show();
              }
          }){
      @Override
      protected Map&lt;String,String&gt; getParams(){
          Map&lt;String,String&gt; params = new HashMap&lt;String, String&gt;();
          params.put(&quot;PARAM_1&quot;, param1);
          params.put(&quot;PARAM_2&quot;,password);
          return params;
      }
  
  };
  
  RequestQueue requestQueue = Volley.newRequestQueue(this);
  requestQueue.add(stringRequest);
  </code></pre>
  <p>What are possible causes for this?</p>