postgres stored procedure json error

So I'm making a application where I want a json string to display(for now). I call a stored procedure with php(which works) and that stored procedure returns a row. The problem is that the record/row that is returned has to be a json string. For that I use php: $verbinding = pg_connect("host=**** port=**** dbname=*** user=******* password=****"); $query = 'SELECT to_json(function_name(parameter))'; $contests = pg_query($query); if(json_decode($contests)) { echo 'succeeded'; } else { echo 'failed'; } Now my code always returns failed and I don't know why or how can I fix this. Thank you in advance for your help!