Marketplace refuses to accept VSIX for 2017 or higher

[pravic]

I can't update this extension on Marketplace due to an obscure error message:

Error: This extension targets Visual Studio 2017 but was not built with an up-to-date VSSDK.

These didn't help:

https://devblogs.microsoft.com/visualstudio/how-to-upgrade-extensions-to-support-visual-studio-2019/
https://docs.microsoft.com/en-us/visualstudio/extensibility/how-to-migrate-extensibility-projects-to-visual-studio-2017?view=vs-2017
http://www.visualstudioextensibility.com/2017/01/10/its-time-to-change-the-vsix-manifest-of-your-extension-to-v3-for-visual-studio-2017-compatibility/

If I add a prerequisites section, it fails with

Error: The file is not a valid VSIX file.