The macOS installer puts the extension in the standard REAPER location, so a portable REAPER never sees it. For a portable install, copy the extension file into the UserPlugins folder that belongs to that REAPER, then restart it. The extension is free.
- In the portable REAPER, choose Options → Show REAPER resource path in explorer/finder. That folder is where this REAPER keeps its settings.
- Open the UserPlugins folder inside it. Create it if it is not there yet.
- Get the file from the setup page:
- macOS: download Portable install (.dmg), open it, and copy reaper_mixsurface.dylib.
- Windows: download the zip, unzip it, and copy reaper_mixsurface.dll.
- Linux: unpack the download and run install.sh with the portable folder, for example
./mixsurface-extension/install.sh ~/opt/REAPER.
- Restart REAPER.
- Open Settings / Preferences → Control / OSC / web, click Add, choose MixSurface and click OK.
Why this happens
- The installer only knows the standard place. On macOS it installs into
~/Library/Application Support/REAPER/UserPlugins/, which a portable REAPER does not read. - MixSurface is not in the Add list. REAPER did not load the file. Check that it sits directly in UserPlugins, not in a subfolder, then quit and reopen REAPER fully.
- Two REAPERs on one computer. Each needs its own copy of the extension, and its own ports. See Run MixSurface against a second REAPER instance.