A method for production of a flat steel product including at least the following steps, completed in a continuous process: providing a flat steel product, wherein a protective metal layer of Zn, a Zn—Al alloy, a Zn—Mg alloy or a Zn—Mg—Al alloy is applied to at least one side by hot dip coating; at least partly removing a native oxide layer present on the surface of the protective metal layer by wetting this surface with an acidic solution of sulfuric acid, sulfurous acid, hydrochloric acid, phosphoric acid, phosphonic acid, nitric acid, formic acid, oxalic acid, acetic acid, citric acid, malic acid, tartaric acid, nitrous acid or hydrofluoric acid; activating the surface of the protective metal layer by applying an aqueous activation solution to the surface of the protective metal layer; and phosphating the activated surface of the protective metal layer by applying an aqueous phosphating solution to the activated surface.