How to get data from a text field created by an app using checkout extension

Topic summary

A developer is working with the Sufio app, which adds a VAT number text field to the checkout using checkout extensions.

Goal:

  • Check if a value exists in the VAT number field
  • If a VAT number is entered, make the “Company” field required

Challenge:

  • Unable to find a way to access data from fields created by third-party apps
  • Research on shopify.dev hasn’t yielded a solution

The developer is seeking guidance on whether it’s possible to retrieve and validate data from checkout fields generated by external applications, as this functionality doesn’t appear to be readily available through standard Shopify extension APIs.

Summarized with AI on November 10. AI used: claude-sonnet-4-5-20250929.

I have an app named “Sufio” which adds a text field in the checkout where users can enter a VAT number. What I want to do is check if there is any value in the VAT number field and if user has entered any VAT number then I want to make the “Company” field as a required field. I tried to research on shopify.dev, if we can somehow access data from fields created by third party apps but it doesn’t seem possible.
Thanks in advance!