File upload for product customization on .json not working

[camiricjey1]

I have used these instructions before to add file upload and custom messages:

https://community.shopify.com/c/shopify-design/product-pages-get-customization-information-for-produc...

But now I am using the "refresh" theme and all endings are on .json instead of .liquid the instructions above aren't matching. Does anyone know the modified steps for this? Thanks!