WeChat public platform developer - WeChat development, php variables in xml cannot be parsed

This is a graphic message returned to WeChat, in which
$item_str
in xml is dynamic, So variables need to be introduced, but it seems that the variables inside cannot be parsed. How to solve this problem?

Reply content:

This is a graphic message returned to WeChat, in which
$item_str
in xml is dynamic, So variables need to be introduced, but it seems that the variables inside cannot be parsed. How to solve this problem?

Variables can be parsed, and sprintf can also be used successfully. The problem lies in the previous variables. The thing I passed in is not an array, so an error occurred. I still need to debug and check more

Use adding points to solve the problem, for example:

<code><Articles>" . $item_str . "</Articles></code>