iPad not casting using Chromecast

Hi,

Have just spent three days trying to cast a downloaded TV programme from my iPad to my TV usinf a Chromecast device. All goes well until the very last step when I get the message that something has gone wrong and to check my internet!!

I have unistalled and reinstalled all relevant apps - Google Home, ITV Hub, rebooted the Chromecast device, a network reboot on my iPad, check the local network settings on my iPad - the list goes on and on.

My iPad connects to my Chromecast dongle, I get the ITV Hub logo appearing on both the TV and iPad screen, I click on the cast icon on my iPad it recognises my TV and all looks OK. Then I click on the play button of the TV program that I wish to play and the system stops and tells me there is a problem and to check my internet connection!

Any ideas

Rgds

PS just downlaoded ios 15 and it hasn't made any difference