Hi @sujitshrestha and welcome to the community! I too am having the problem that when trying to download media attachments via Zip file I only ever get ‘failed’.
It seems to be a problem introduced in the last release - I can see that others have logged this issue too. It looks like the KoBo team are working on it, but in the meanwhile their suggested workaround is to download the attachments separately:
All the best
