@smmoniruzzamann, without providing a proper URL, where the download fails, it's extremely hard to help you in solving this issue. Please provide the URL, so opera developers can take a look.

@smmoniruzzamann

This dialog is introduced to protect you from leaving the free-internet. It's great you have spent your time for reporting the issue and helping developers making Mini the better browser. Thank you!

Could you help us even more and provide the url, where the problem occurs, please? Do you have any balance on your SIM card? Did you try downloading with a different browser to verify it's not a server issue?