I would advise everyone to use https://wetransfer.com/ to upload files. This is the best server and does not limits download speed, files up to 2GB can be uploaded in one go,but you can upload as much as you like.
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How to fix “not a valid application” error [iPhone/iPod/iPad] ?
1.Use WinRAR (the best) or similar program to fix the file: You will find in Tools menu >> Repair Archive, just click on this option, after repair reopen the file (.ipa) with iTunes. For about 80% of such errors, this will fix the problem; if you still having the same error try method 2,
2.Redownload the application “ .ipa file “ and make sure that the uploader is not the same one “you can know that from the file name, usually you will find the uploader name at the end >>