For packaging conformity, there is nothing to produce: reusing a box you have received does not constitute placing it on the market again, and the obligations (technical documentation and declaration) have already been handled upstream when it was first placed on the market. This does not make you a packaging manufacturer. There are two qualifications, however. First, you almost always add less visible packaging (adhesive tape, void fill, tissue paper and mailing sleeves): buy these from suppliers established in France or the Union and keep your invoices. Second, the French EPR declaration remains required for every parcel shipped to a private individual, whether the packaging is new or reused, and it gives you the unique identifier now requested by marketplaces.
Read the source article: PPWR small business obligations: the micro-enterprise rule