Json data received by url in api-php, json_decode is empty

# The result of json data decode in the php background is empty # I use a mobile phone to transmit data to the php background, and the result of json_decode is empty. The mobile phone transmission method is POSTGET, encoding format is UTF-8. Json data is (including single quotation marks in the code, which are transmitted using strings. json data must be double quotation marks): & quot; & #39 ;{& quot; agent & quot ;: & quot; 30 & quot;, & quot; job & quot;: & quot; 1133 & quot;, & quot; students & quot;: [{& quot; working_hours_un phpapijson: communication between the mobile phone server and the client

# Php background json data decode is empty #
I use my mobile phone to transmit data to the php background. the result of json_decode is blank.
The mobile phone transmission method is POST/GET, the encoding format is UTF-8.
Json data is (including single quotation marks in the code, which are transmitted using strings. json data must be double quotation marks ):

   '{"agent":"30","job":"1133","students":[{"working_hours_unit":"null","working_hours":"6","student_id":"191","commission_unit":"null","wage":"58","commission":"348","wage_unit":"null"}]}'

The php code obtains the preceding json data and can use echo to output the data. Php code:

 $str=$_GET('my_str'); echo $str;

Output the test result and then decode the received json data. Code:

 $form = json_decode($Noel,true); var_dump($form);

Unexpectedly, the output is ** null **. then, I use _ echo json_last_error (); _ to output a json conversion error with the result of 4 = json syntax error.
Complete Code and:

     $str=$_GET('my_str');  echo $str;$form = json_decode($str,true); var_dump($form); echo json_last_error();

However, when I separate the received json into the PHP code, the decode can be correctly parsed. (In my heart, the crash _ crash)
Code :'

     $orm='{"agent":"30","job":"1133","students":[{"working_hours_unit":"null","working_hours":"6","student_id":"191","commission_unit":"null","wage":"58","commission":"348","wage_unit":"null"}]}';  $arr=json_decode($form,true);  var_dump($arr);

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