When we mirror from iPad to Sony Bravia tv we get sound but no picture

Are you attempting to “mirror” your iPad to your TV using AirPlay, or an HDMI cable connection? Does your TV support AirPlay/AirPlay2 - and if so, are both your iPad and TV connected to the same WiFi network?

Be aware that very few USB-C HDMI adapters/hubs support HDCP 2.0 - absence of which will inhibit the ability to output copy-protected HD media content from iPad to a connected monitor/TV over an HDMI connection. 

The Apple USB-C Digital AV Multiport Adapter does support HDCP 2.0, but perhaps lacks some of the additional the flexibility afforded by some third-party USB-C hubs:

https://store.apple.com/uk/xc/product/MUF82ZM/A

Note also that some iPad models that feature USB-C also support DisplayPort Alternate Mode over USB-C. This protocol allows direct connection, with an appropriate Thunderbolt cable, to a monitor that supports DisplayPort - removing the need for HDMI.

That generally indicates the app does not support AirPlay mirroring for its content.

What App are you trying this on?

Are you starting the AirPlay from Control center, or from the mirror option within the App?