View source for Talk:REST/@comment-84.88.66.194-20140407152544/@comment-82.198.197.57-20140519100400

First, the custom field must be created inside RT, the REST API does not create new custom fields. It only fills existing ones.

Second, the prefix CF- seems to be wrong. Try using CF.{FieldName}, that works for me (I'm using Java). So in PHP this should be:

$content = array( "CF.{admin-keywords}" => "Keyword name" );

If you request info about a ticket, the custom fields are written like this instead of the documented CF- prefix.