What is a supplier's declaration?
A supplier's declaration is your supplier telling you, in writing, where the material they sell you originates. You need it before you can count a bought-in material as originating.
Why they matter
Most producers buy in most of their inputs. Without a declaration you can't show those inputs originate, so they're treated as imported, and that can be the difference between qualifying and not.
Long-term declarations
Rather than one per delivery, many agreements accept a single declaration covering repeat supplies for up to a year or two. It has to be kept up to date if anything changes.
Chasing them
Collecting declarations is usually the slow part. In Inferred, suppliers answer requests in their own account and each declaration is checked against the agreement as it comes in. You approve every result.