while i am trying to upload a zip file to restore course, it prompting an error as invalid json string.
its very urgent.
any help would be appreciated!
Which version of Moodle? Is this any file or just 'big' ones (close to or over the maximum upload file size)?
There's a lengthy discussion here which might give you some insight...
Failing that, you are welcome to PM me details of enough (temporary) access to your site to try it and I'll check for errors for you.
Unfortunately you don't provide much info (besides the Moodle version): Present facts and background in your post