How do I solve error : "@parcel/transformer-postcss: PostCSS config must have plugins"

Building my project with parcel I got this error:

@parcel/transformer-postcss: PostCSS config must have plugins

at load ([projectpath]/node_modules/@parcel/transformer-postcss/lib/loadConfig.js:166:13)

This happened since when I upgraded parcel. Not very clear to me , how should I set plugins I tried adding a .postcssrc json file on the project

(Added at the location from where I issue a "parcel build ...", but it seems that it doest see it, since I get a message like: Using a javascript PostCSS config file means losing... Use a .postcssrc json file whenever possible)

.postcssrc json file contents:

{
  "modules": true,
  "plugins": {
    "autoprefixer": {
      "grid": true
    }
  }
}