Unable to dynamically link forms in Kobotoolbox

I am building XLS forms and trying to dynamically link the parent form to the child form. But for some reason this time I am unable to link the two (i have been successful in the past). I Shall add the files here for reference.
Can someone help me identify where I went wrong.

https://drive.google.com/drive/folders/1v5-sZLLxhBQZKkxFB9DDEC81q-JDrdW-?usp=sharing

Welcome to the community, @antonyjohn! Have you gone through the support article shared below?

Have you tested the sample XLSForm that has been shared in the support article? The attached sample support article should help you understand how the expressions for the dynamic data attachment can be built.

Yes I have gone through the same. But still no success.