@type t() :: %PolarExpress.Schemas.CustomerUpdateExternalID{
  billing_address: PolarExpress.Schemas.AddressInput.t() | nil,
  email: String.t() | nil,
  locale: String.t() | nil,
  metadata:
    %{
      required(String.t()) => String.t() | integer() | float() | boolean() | nil
    }
    | nil,
  name: String.t() | nil,
  tax_id: [String.t() | PolarExpress.Schemas.TaxIDFormat.t()] | nil
}

• billing_address - Nullable.
• email - The email address of the customer. This must be unique within the organization. Nullable.
• locale - Nullable.
• metadata - Key-value object allowing you to store additional information.

The key must be a string with a maximum length of 40 characters. The value must be either:

• A string with a maximum length of 500 characters
• An integer
• A floating-point number
• A boolean

You can store up to 50 key-value pairs.

• name - Nullable.
• tax_id - Nullable.