If the plug-ins included with Samplitude Pro X3 are not appearing, there was most likely a problem during installation.
Start by checking the installation path.

VST3

• C:\Program files\Common files\VST3 (64bit)
• C:\Program files x86\Common files\VST3 (32bit)

VST2

• C:\Program Files x86\Common files\VstPluginsVST2 (32Bit)
• C:\Program Files (x86)\Common Files\Vst2VST2 (32Bit)
• C:\Program Files (x86)\VSTPlugins\MAGIX\ (32Bit)
• C:\Program Files\Common Files\VST2 (64 Bit)
• C:\Program Files\VSTPlugins\MAGIX\VST2 (64 Bit)

When installing the plug-ins, we recommend performing a custom installation and installing all the plug-ins in a folder you created yourself.
For example: "C:\Audio\VstPlugins":

• C:\Audio\VstPlugins\32bit
• C:\Audio\VstPlugins\64bit
• C:\Audio\VstPlugins\VST3_32
• C:\Audio\VstPlugins\VST3_64

It is not possible to install VST3 in a custom folder. 
However, you can manually move the dll files into the folder of your choice after installation.

• In Samplitude, press the Y key to open the System Settings and go to "Effects" > "VST / Rewire".
• Select the plug-in folder you created (e.g. C:\Audio\VstPlugins).

Samplitude will automatically access all subfolders as well. Do not miss to activate the option "Scan user and system VST folders automatically for new plug-ins". This option is important if you installed your plug-ins to their default installation folder: "C:\Program Files\Common Files\VST3". 

All subfolders are allowed to contain other subfolders, which can be organized according to plug-in type and manufacturer name (e.g. C:\Audio\VstPlugins\64bit\EQ\FabFilter).

The VST plug-ins are not showing up even though the installation path is correct

To fix this problem, follow these steps:

• Delete VSTPlugin.ini from the Samplitude installation folder and scan the folder again.
• Plugin.dll files can also be manually registered and dragged from the plug-in folder in Windows File Explorer onto the program interface.
• If you are using Windows 7, it may help to delete the file "sam.exe" from the Samplitude installation folder.
• Install the plug-in as an administrator.

It's also possible for plug-ins to conflict when being imported using the default VST bridge and to be set to "invalid" (represented by the numeral 4 at the end of the VSTPlugins.ini file).  

Open "VSTPlugins.ini" in Notepad and search for the installed plug-ins. 
Check to see whether any of the entries have a 4 at the end of them. 
If they do, you can manually change them as follows:

• 32-bit plug-ins
  For effects = 0
  For VSTi      = 1
• 64-bit plug-ins
  For effects = 64
  For VSTi     = 65

The "VSTPlugins.ini" file is located here:

• Sam ProX / Sequ 12:
  ...MAGIX\Samplitude_Pro_X\_ProgrammData\VstPlugins.ini
• Samplitude 11 / Sequ 11 and older versions:
  ...Magix\Samplitude 11 Pro\VstPlugins.ini
  ...Magix\Sequoia 11\VstPlugins.ini