rexml becomes explicit dependency as of Ruby 3.0

[2called-chaos]

Other notable changes since 2.7

• The following default gems are now bundled gems.
  • rexml

via

Causing

LoadError: cannot load such file -- rexml/document
[..]/ruby/3.0.0/gems/activesupport-6.1.3.2/lib/active_support/dependencies.rb:332:in `require'
[..]/ruby/3.0.0/gems/activesupport-6.1.3.2/lib/active_support/dependencies.rb:332:in `block in require'
[..]/ruby/3.0.0/gems/activesupport-6.1.3.2/lib/active_support/dependencies.rb:299:in `load_dependency'
[..]/ruby/3.0.0/gems/activesupport-6.1.3.2/lib/active_support/dependencies.rb:332:in `require'
[..]/ruby/3.0.0/gems/amazon_pay-2.6.1/lib/amazon_pay/response.rb:1:in `<top (required)>'

Fix

Add gem 'rexml' to your Gemfile (maybe with a version restriction)

this is mainly for others googling this :)