Change_column_value NOT WORKING in python

I tried to update column value via Monday API with python. However, it is not working.
Here is my code:

query = 'mutation { change_column_value (board_id:721223202, item_id: 759890643, 
          column_id: "text7", value:"\"Sample Text\"") { id }'

data = {'query' : query}
r =, json=data, headers=headers) # make request  

The exactly same query works in online graphQL editor, but not in python.
The error message as follows:

{'errors': [{'message': 'Parse error on "" (STRING) at [1, 105]',
   'locations': [{'line': 1, 'column': 105}]}],
 'account_id': 6978649}