Whatsapp mail restore messages - from iphone to android

[Android Central Question]

Hello, I moved to android (oneplus) from Iphone. I want to export and import just few chats history.
I was following the process with the iphone-sending by mail the txt files then download it to the new OnePlus and then open Whatsapp but its not letting me restore the files.
Its says something about my mail.
Any idea how to resolve this?
Thanks!