use windows api c# set primary monitor

i'm perplexing windows api set primary monitor. doesn't seem work - shade only flicks zero happens.

    open const int dm_orientation = 0x00000001;
public const int dm_papersize = 0x00000002;
public const int dm_paperlength = 0x00000004;
public const int dm_paperwidth = 0x00000008;
public const int dm_scale = 0x00000010;
public const int dm_position = 0x00000020;
public const int dm_nup = 0x00000040;
public const int dm_displayorientation = 0x00000080;
public const int dm_copies = 0x00000100;
public const int dm_defaultsource = 0x00000200;
public const int dm_printquality = 0x00000400;
public const int dm_color = 0x00000800;
public const int dm_duplex = 0x00001000;
public const int dm_yresolution = 0x00002000;
public const int dm_ttoption = 0x00004000;
public const int dm_collate = 0x00008000;
public const int dm_formname = 0x00010000;
public const int dm_logpixels = 0x00020000;
public const int dm_bitsperpel = 0x00040000;
public const int dm_pelswidth = 0x00080000;
public const int dm_pelsheight = 0x00100000;
public const int dm_displayflags = 0x00200000;
public const int dm_displayfrequency = 0x00400000;
public const int dm_icmmethod = 0x00800000;
public const int dm_icmintent = 0x01000000;
public const int dm_mediatype = 0x02000000;
public const int dm_dithertype = 0x04000000;
public const int dm_panningwidth = 0x08000000;
public const int dm_panningheight = 0x10000000;
public const int dm_displayfixedoutput = 0x20000000;

public const int enum_current_settings = -1;
public const int cds_updateregistry = 0x01;
public const int cds_test = 0x02;
public const int cds_set_primary = 0x00000010;

public const enlarged disp_change_successful = 0;
public const enlarged disp_change_restart = 1;
public const enlarged disp_change_failed = -1;
public const enlarged disp_change_badmode = -2;
public const enlarged disp_change_notupdated = -3;
public const enlarged disp_change_badflags = -4;
public const enlarged disp_change_badparam = -5;
public const enlarged disp_change_baddualview = -6;

    open stationary vacant setprimary(screen screen)
{
  display_device d = new display_device();
  devmode dm = new devmode();
  d.cb = marshal.sizeof(d);
  uint deviceid = 1;
  user_32.enumdisplaydevices(null, deviceid, ref  d, 0); // 
  user_32.enumdisplaysettings(d.devicename, 0, ref dm);
  dm.dmpelswidth = 2560;
  dm.dmpelsheight = 1600;
  dm.dmpositionx = screen.bounds.right;
  dm.dmfields = dm_position | dm_pelswidth | dm_pelsheight;
  user_32.changedisplaysettingsex(d.devicename, ref dm, intptr.zero, cds_set_primary, intptr.zero);
}

i slight this:

setprimary(screen.allscreens[1])

any ideas?