I am trying to update some cells in an existing SmartSheet sheet with PHP. It's no problem to add new lines but I can't get the correct JSON for updating. My code at this moment: $ch = curl_init("https://api.smartsheet.com/1.1/sheet/1234567890/rows/"); $header = array("Authorization: Bearer xxxxxxxxxxx", "Content-Type: application/json", "Assume-User: xxxx%40xxxx.com"); $name = 'MyName'; $fields = '{"rowNumber":1, "columnId": 1234567890, "value": "'.$name.'", "displayValue": "'.$name.'"}'; curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); curl_setopt($ch, CURLOPT_HTTPHEADER, $header); curl