As per the [contributing guide](https://github.com/Shopify/active_merchant/wiki/contributing#wiki-options-hash), the correct way to assign currency would be:
```ruby
post[:currencyCode] = options[:currency] || currency(money)
```
This applies to the two other places you are assigning `post[:currencyCode] = ..` also.

I don't believe the `unless` conditional wrapper is required, let's default to always passing the default currency or allow the currency to be overridden by the options hash.