How to add flexible fields to the Supplier Portal in the section to create an invoice?

Summary:

Can the supplier portal page be customized with DFF from invoice creation?

Content (required):

Users request that two new fields be created within the invoice creation page in the supplier portal, and that the description field be mandatory. I want to know if this is possible and how this request could be made.

I would greatly appreciate your help.

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Code Snippet (add any code snippets that support your topic, if applicable):