B-Chat App runs on Android Devices with Version 5.0 Lollipop upto Android Oreo 9.0+ & iOS Devices with Version 11.0+ to latest.
Android: Select Left Menu > and then select Contacts options > And then click on the button that says sync contacts.
iOS: Select Settings > Then click on Sync Contacts
If your chats are not appearing, quit the app and then relaunch the app, if this does not fix the issue, re-install the app from the store. If it still does not fix your problem, you can report the issue here.
There is a limit of file size of 60mb for all kinds of media, make sure your file size is less than 60mb in size to ensure the media gets delivered succesfully.