For galvanised steel the traditional primer to use is Calcium Plumbate although some water based alternatives such as ‘Dulux Metalshield Quick Drying Metal Primer’ can work just as well.
Newly galvanised metal does pose a problem with painting though because the surface is often too smooth for paint to key to. Acid based etching primers can be used, if it’s absolutely necessary, although allowing the surface to weather over time can be just as effective.