How to upload multiple pictures to Volusion through API

This is my Volusion item insert method, which relies on the HTTParty gem for rails. It works for posting items without photos, and posting items with a single photos by using the <PhotoURL_Large> and <PhotoURL_Small> XML tags.

def self.post_volusion_item(hide_product, product_code, product_name, product_description, availability, custom_field1, custom_field2, enable_options_inv_control, free_shipping_item, height, length, width, metatag_description, metatag_title, photo_alt_text, photo_xml, product_category, product_price, product_weight, metatag_keywords)
  encrypted_password = ENV['VOLUSION_PASSWORD']
  post_url = "https://WEBSITE-HERE/net/WebService.aspx?Login=LOGIN-HERE&EncryptedPassword=#{encrypted_password}&Import=Insert"
  body = "<?xml version=\"1.0\" encoding=\"utf-8\" ?><Volusion_API><Products><HideProduct>#{hide_product}</HideProduct><ProductCode>#{product_code}</ProductCode><ProductName>#{product_name}</ProductName><ProductDescription>#{product_description}</ProductDescription><Availability>#{availability}</Availability><CustomField1>#{custom_field1}</CustomField1><CustomField2>#{custom_field2}</CustomField2><EnableOptions_InventoryControl>#{enable_options_inv_control}</EnableOptions_InventoryControl><FreeShippingItem>#{free_shipping_item}</FreeShippingItem><Height>#{height}</Height><Length>#{length}</Length><Width>#{width}</Width><METATAG_Description>#{metatag_description}</METATAG_Description><METATAG_Title>#{metatag_title}</METATAG_Title><Photo_AltText>#{photo_alt_text}</Photo_AltText><PhotoURL_Large>#{photo_url_large}</PhotoURL_Large><PhotoURL_Small>#{photo_url_small}</PhotoURL_Small><ProductCategory>#{product_category}</ProductCategory><ProductPrice>#{product_price}</ProductPrice><ProductWeight>#{product_weight}</ProductWeight><METATAG_Keywords>#{metatag_keywords}</METATAG_Keywords></Products></Volusion_API>"

  post(post_url, body: body)
end

I can not find any documentation that gives an example with multiple photos in the item. I have tried duplicating the calls. Example: <PhotoURL_Large>img1</PhotoURL_Large><PhotoURL_Small>img1</PhotoURL_Small><PhotoURL_Large>img2</PhotoURL_Large><PhotoURL_Small>img2</PhotoURL_Small>

This resulted in no images uploading.

I am realizing the the PhotoURL is not related to the urls of the item's photos, but only tied to the data in Volusion's add item form.

Can someone point me in the right direction for accessing the true photo urls for volusion items?