Hello there! I would like an application which also uses the extension

solidus_multi_domain

to Solidus 3.0. This extension is said on https://solidus.io/extensions/ to support Solidus 3.1 and 3.2, but when I try to bump up my versions, the Bundler complains saying that the extension only accepts

solidus_core

versions lower than 3. Am I missing something? Thank you in advance!

There hasn't been a release cut in a while. The master branch supports newer versions of Solidus, but the latest version on Rubygems doesn't. You can just point your Gemfile at GitHub.