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Unfortunately, only that user if (s)he chooses to send you back can do that.

But hé has nothing, no post no comment, nothing, he looks like he doesn't exist

Which means someone created that account to benefit from accidental transfers like yours.

Can you or hive do something for this accidently case?? 63 hive , it's lot for me 2 months of work
Perhaps he isn't on hive anymore

This is decentralized network only you have access to your account and your wallet. Next time please be careful. Unfortunately those funds are unrecoverable unless receiver chooses to send it back. There is nothing we can do.

I have no way to contact him, can you contact him if you can of course, Thanks