Getting "Missing ID in manifest.json" when I do have an ID

I’m trying to publish my plugin and seeing the above error message despite the fact that I do have an ID in my manifest file. The current ID was generated from a previous publish attempt where clicking “Generate ID” solved the problem - as such it can’t be that the ID is in the wrong format as it was generated by Figma to begin with.

I don’t want to have to generate it again as it will break some of the connections to plugin data that I have set.

Here is a slightly altered copy of my manifest file:

{
      "id": "958864801345787601",
      "name": "My Plugin",
      "api": "1.0.0",
      "main": "code.js",
      "ui": "index.html"
}