"Plugin not found" error trying to install WPGraphQL Smart Cache

[upsidefoods]

Hi! I'm trying to install the WPGraphQL Smart Cache extension from the WPEngine page (GraphQL | Extensions | WPGraphQL Smart Cache | Install & Activate). I get a red error bar that says "Plugin not found." If this helps, I see a POST from my browser to:

https://upsidewebstg.wpengine.com/wp-json/wp/v2/plugins?_locale=user

And this returns a 404, with body: {"slug":"wp-graphql-smart-cache","status":"inactive"}

Am I doing something wrong? Is there an alternate way to install the plugin?