@spec generate(
  params,
  keyword()
) :: {:ok, String.t()} | {:error, Paddle.Error.t()}
when params: %{
       optional(:product_id) => integer(),
       optional(:title) => String.t(),
       optional(:webhook_url) => String.t(),
       optional(:prices) => [String.t()],
       optional(:recurring_prices) => [String.t()],
       optional(:trial_days) => integer(),
       optional(:custom_message) => String.t(),
       optional(:coupon_code) => String.t(),
       optional(:discountable) => boolean(),
       optional(:image_url) => String.t(),
       optional(:return_url) => String.t(),
       optional(:quantity_variable) => boolean(),
       optional(:quantity) => integer(),
       optional(:expires) => String.t(),
       optional(:affiliates) => [String.t()],
       optional(:recurring_affiliate_limit) => integer(),
       optional(:marketing_consent) => boolean(),
       optional(:customer_email) => String.t(),
       optional(:customer_country) => String.t(),
       optional(:customer_postcode) => String.t(),
       optional(:passthrough) => String.t(),
       optional(:vat_number) => String.t(),
       optional(:vat_company_name) => String.t(),
       optional(:vat_street) => String.t(),
       optional(:vat_city) => String.t(),
       optional(:vat_state) => String.t(),
       optional(:vat_country) => String.t(),
       optional(:vat_postcode) => String.t()
     }