Ask HN: Full featured third party chat/messaging solutions for a mobile app?

I am making a mobile app and want to have a chat/messaging feature where users can directly chat with me (in order for them to ask questions about a product) in real time. I would also like to have file exchange support (to send imgs, PDFs, etc) within the chat.. I know it maybe a stretch but are there are third party solutions that offer this feature?? So far the closest thing that is still far from what I want is firebase cloud messaging.