You can only load 3rd party VST Plugins by using the following Studio One versions:
Studio One (4 or below) Producer/Professional
Studio One 5 Artist/Professional
Please refer to the articles below for more information:
How do I add a 3rd party VST to Studio One?
On macOS:
1. Log into the download page, download & install the AU/VST version of BIAS FX 2.
2. Launch Studio One and navigate to Studio One -> Preferences -> Locations -> VST Plug-ins:
3. Make sure the correct location is added:
VST : /Library/Audio/Plug-ins/VST/
Audio Unites : /Library/Audio/Plug-ins/Components/
4. Please tick the Scan at startup option, and make sure Studio One scans your plug-ins at the program startup.
5. Now refer to this video here to record your guitar track with input monitoring. (In this video, Studio One's built-in amp simulator is used. Just replace it with BIAS FX 2 and you're good to go)
On Windows:
1. Log into the download page, download & install the 64-bit version of BIAS FX 2.
2. Make sure the VST/VST3/AAX files are installed in the following paths:
If you'd like to change the install location for a specific section, please click the corresponding "Browse" button on the right.
*We'd strongly recommend keeping the install location as default.
3. Launch Studio One and navigate to Studio One -> Options -> Locations -> VST Plug-ins2) Make sure the correct location is added. The location of plug-in files depends on your setting during installation.
The default locations are as follows:
C:\Program Files\VstPlugins
4. Please tick the Scan at startup option, and make sure Studio One scans your plug-ins at the program startup.
5. Now refer to this video here to record your guitar track with input monitoring. (In this video, Studio One's built-in amp simulator is used. Just replace it with BIAS FX and you're good to go)
For Mac & Windows
Reset Blacklist
Navigate to the "Studio One" drop-down menu, select "Options under the "Locations" tab-> click "Reset Blacklist".
Further reading:
BIAS FX 2 Plug-in Display Issues on Windows: Cut Off or Too Large