I think it would be a good idea to add the minRackVersion key to the manifest, e.g. "minRackVersion": "2.6.0" to avoid this in the future. Described here in the manual, it’s designed to express the minimum Rack version that the plugin needs, and I presume there’s a bit of UI in Rack around it, to warn the user that their version of Rack doesn’t support this plugin. See e.g. the Fundamental manifest using it.
You shouldn’t because you could not have known about this incompatibility, although, for reasons like this example, it’s generally a good idea to upgrade Rack to the latest version, when the red dot appears in the Help menu, from which you can directly get it and upgrade.