Package is invalid: 'CRX_REQUIRED_PROOF_MISSING'

[NicolasGuilloux]

When Chromium based browser loads the packed extension, it refuses to load it and displays the following line: Package is invalid: 'CRX_REQUIRED_PROOF_MISSING'.

I tried with Brave, Chromium and Google Chrome and it is the same. I even tried to package the extension from the browser menu. It packages it but when it loads into the browser, it displays the same message.