Butter Motion has a small desktop app that lives outside Premiere. You install it once, sign in there, and it sets up the plugin inside Premiere for you. After that you mostly forget it exists: it sits quietly and lets you know when something needs your attention.
What it does
Signs you in. The app is where you sign in the first time, before anything else is installed.
Installs the plugin. Once you're signed in, the app downloads and sets up the plugin inside Premiere Pro.
Keeps things updated. It tells you when a new version of itself is out, and the plugin updates itself from inside the panel.
Shows your account. Plan, credits and a shortcut to your account page, without opening a browser.
Removes the plugin cleanly. One button removes the plugin and its Premiere panel. The app and your account stay.
What you'll see
The app walks you through a short setup the first time you open it:
Sign in. "We'll open your browser. Approve this computer there." Click Sign in via browser, approve the computer, and you're back in the app automatically.
Install Butter Motion. Click Install. The app downloads and sets up the plugin, moving through stages from Downloading to Starting.
Everything's ready. "Butter Motion is installed and ready in Premiere Pro." Restart Premiere and open the panel.
If an install breaks, the app opens the setup screen with Reinstall and Copy diagnostics right in the install step. Later you can copy the same summary in Help, with Copy in the Diagnostics row. It's a text summary of your app version, channel, plugin state and version, OS, and the plugin's recent log, so you or support can see what happened. See Contact support.
Where to get it
Download the app from your account's Downloads page. There's one installer per operating system.
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On Windows a blue "Windows protected your PC" screen may show up the first time you open the app. What to click is on Install on Windows.