Yoast SEO Premium is an add-on. The free Yoast SEO plugin does the work, and Premium adds the extras on top. Install both.
Install
- Upload and activate Yoast SEO, the free version.
- Upload and activate Yoast SEO Premium.
- Add your update key to the 99Plugs Update Manager. See How to enable auto updates.
Both files come with your purchase and both are in My Downloads in your account dashboard on 99plugs.com. You can also install the free half straight from Plugins → Add New Plugin in WordPress.
If the Premium features are missing
The free plugin is not active. Premium has nothing to attach to on its own, and this is what it looks like when it is missing. The pattern is explained in Why some plugins need the free version installed too.
The activation prompt
Yoast will ask you to activate your subscription. Skip it. The plugin works without it, and your updates come through the Update Manager instead. See My plugin or theme is not activating.