In-app Chat API and SDK

I am developing an app with in-app messaging features and require a chat API and SDK. We have narrowed our options down to three affordable providers: Mirrorfly[https://www.mirrorfly.com/chat-api-solution.php], Apphitect, and Weavy. I need to select one that offers robust customization and white-labeling capabilities. I would appreciate suggestions from anyone who has experience using these products.