Whats is Certificates of Origin?

When exporting to an FTA partner market, claiming preference allows your qualifying U.S. products to receive lower tariff rates under the agreement.

Not all U.S. FTA agreements require specific forms to claim origin. Most of our FTA partners can accept statements that include specified data elements that explain how the product qualifies for the agreement. But the importer may ask you to use a specific format. 

Claiming FTA preference allows qualified U.S. products to be more competitive through reduced or exempted duties (tariffs), although local taxes still apply. FTA certifications are optional, and not required for shipments to clear customs. However, goods shipped without one may be assessed standard tariff rate, so be sure to include an FTA certification of origin. For shipments below $2,500, the exporter should indicate on an invoice that a product is of U.S. origin and qualifies for an FTA. For Israel, U.S. exporters or producers may need to complete and sign the U.S. Origin Invoice Declaration.

source: https://www.trade.gov/fta-tariff-tool-home