inavalid data type msg when inserting a variable into custom field

[MarieF38]

I am trying to insert a string through a variable into a custom field.

$contact->custom_fields = array(array('name' => 'CustomField1', 'value' => $_POST['type_of_book']));

Inserts fine.

The code below:

$foo=$_POST['type_of_book'];
$contact->custom_fields = array(array('name' => 'CustomField1', 'value' => $foo));

Results in the following error msg.

[error_key] => json.type.invalid
            [error_message] => #/custom_fields/0/value: Value is of a disallowed type. Allowed types are: Null, String.

I need the variable because the it will contain multiple values from an imploded checkbox array.

Please advise why this generates an error?

[DaveBerard]

What is the value of $foo?  If it is a boolean (true/false), PHP will serialize that to a boolean JSON value which is not valid for that field.  You would need to pass in a string value for true/false if you wanted to store that in the custom field.