when plugins has options,it can't work

[fsy0718]

  plugins: [
        postcssEach({
          plugins: {
            afterEach: ['postcss-at-rules-variables'],
            beforeEach: [postcss-custom-properties({
                importFrom: [
                   customProperties: {
                       '--test-color': red
                  }
               ])]
          }
        })
  ]

the errors:

[Error] Error: Use process(css).then(cb) to work with async plugins

[adamduncan]

I came across trying the plugin for the first time today too. Attempting to call postcss-custom-media before/afterEach.

Is there something we're doing wrong here, or something unsupported at the package level?