At least 48 hours before you bring a dangerous mixture on the Belgian market, you should make a notification to the Poison Centre. This applies to products you sell to the general public, as well as products intended for professional use. You must also pay a fee of € 200 (variations are possible; see the Royal Decree on paying fees and contributions, in Dutch or French).
From January 1, 2020, importers and downstream users should declare their dangerous mixtures systematically using a harmonised format. More information is available on the ECHA site on Poison Centers.