Trains and metros (50 and 51) stop at Amsterdam Zuid station. Leave the station via the south exit (Gustav Mahlerplein / ABN AMRO exit), which will take you to the large Gustav Mahlerplein square.
When you leave Amsterdam Zuid station on the south side, walk straight across Gustav Mahlerplein, between ABN AMRO and the ITO Tower. At the end of the square, cross Gustav Mahlerlaan. On your left is the red-brown Symphony building, which houses the Dutch Payments Association. Please report to the central reception desk.