Make sure that your swift-tools-version is correct. When you create the Vapor project, open Package.swift. On line 1 update the comment to your current specifications.  

Here is a message from an actual student:

I found that if the current swift-tools-version in your machine is lower than the one specified in the comment at Package.swift line 1 the packages are not going to be downloaded and you could not build the project at all

To solve this, update the comment to your current specifications (I had to update from // swift-tools-version:5.8 to 5.6. Then I had to update .macOS(.v13) to (.v12)