How to fix InvenTree plugin install: ERROR: You must give at least one requirement to install (see "pip help install")

Problem

You want to install a plugin in InvenTree from a git repository:

but you see the following error message:

ERROR: You must give at least one requirement to install (see "pip help install")

Solution

You must use git+https instead of just https as URL, e.g.

git+https://github.com/ulikoehler/InventreeBrotherQLLabelPrintServicePlugin.git