Send Control Number For USPS First Class letter to MarketPlaces

When we ship First class mail LETTER USPS generates a Control Number that used to be sent to eBay for example with the new version is not doing it anymore, that way the customer sees a number, now that is not doing it I get 30 to 40 emails a day asking for it, before they just see it and only those who click it asked and we explain that due to weight and value it as sent as a letter. It is REALLY a problem now that is not doing it.