TPL Hook not working

I added a TPL hook to get me a field in the product update but it is not working. I have also cleared the cache. Could not find any post on the forums that can help. Any help would be appreciated.

Hook path: cscart/design/backend/templates/addons/custom_product/hooks/products/update.pre.tpl
app addon path: cscart/app/addons/custom_product (includes controllers & schemas folder)

Looks like there is no such a hook in the default file


For example, you can try