Structured data (schema)
A hidden record in the page explaining to a machine what the content is: a product, an article, a company. Copied identically everywhere, it brings no benefit.
Why it matters when you read an offer
Made for the specific page, it helps machines understand what exactly you sell. Copied identically everywhere, it is a reliable sign that nobody looked at your site page by page.
What it looks like in an offer
Adding schema for a separate fee. Ask which types, on which pages and why those: the listing is the test of whether a plan exists.