Rails: Why is the "number_with_delimiter" method not recognized inside my model?

You should use extend:

Usage: extend ActionView::Helpers::NumberHelper

It is good for me

The true problem here is that you're including this module into the class, rather than extended the class with it.

The differences is an include will make the methods available on the instance, where as the extend will make them where you're trying to use them: on the class.

For instance method use

include ActionView::Helpers::NumberHelper

For class method use

extend ActionView::Helpers::NumberHelper

You might be missing the dependency... is the NumberHelper class accessible to your application?

Check the official Rails docs

Instead of extending ActionView module. You can use methods from ActiveSupport instead

For example:

ActiveSupport::NumberHelper::number_to_currency(10000.1234,{precision: 2,unit: ''})