No backup found - WhatsApp

Hey there.

So I need to send my iPhone X for repair (faulty screen).

I need to have a phone with me and WhatsApp, so I wanted to use my iPhone 6s.

I did a WhatsApp backup and it shows up on iCloud->manage storage.

when I launched WhatsApp on my iPhone 6s its shows “no backup found” but it’s clearly existing...

I deleted WhatsApp on my iPhone X and reinstalled it and on my iPhone X the backup does show up.

tried setting my 6s from a backup of my x... no luck there as well... I can’t send my X till I set up WhatsApp on my 6s ... help me please