How to Transfer WhatsApp Chat Data and Photos/videos from iPhone to Android
1. Backup the iPhone with iTunes or use a freesoft: CopyTrans Shelbee (via the control center)
when you are prompting to Install Whatsapp (older version) don't forget to allow unknown source...
Important: open google chrome and ensure that you dont have any open tabs with any website. if you do - close them all.
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didn't try, seems more complicated!