This is the method definition of the running branch:
```ruby
def transliterate(string)
  string.mb_chars.normalize(:kd). # Decompose accented characters
        gsub(/[^\x00-\x7F]+/, '')     # Remove anything non-ASCII entirely (e.g. diacritics).
end
```

The problem is $KCODE is set to "NONE", and in that case mb_chars returns a Ruby String instead of ActiveSupport::Multibyte::Chars, which doesn't have a normalize method. The proposed solution was to set $KCODe = 'u' as in https://github.com/Shopify/active_merchant/blob/master/lib/active_merchant/billing/gateways/garanti.rb#L1 (While not a fan of modifying a global variable, I guess it is an acceptable solution)