Whatsapp: cannot add friend to contacts

I recently reset my Samsung galaxy s7 edge so all of my contacts in WhatsApp were removed. I have now reinstalled the app and made sure it is up to date. When I open the app I can see that me and my friend have an open chat, just you would normally see if you were friends with someone. But the difference in my case is that it says "The sender is not in your contact list", which makes sense because everything got erased after the reset. I therefore click "add to contacts", and click "existing" to add an existing account, find my friends number from the phone book and then add. The problem though is that it won't save this procedure, so it still says that my friend is not in my contacts. Clearly there seems to be some bug involved here. I've also tried to add as a new contact and type phone number and name manually, but still it won't save.
Any input is appreciated.

FIX: clicked on contact list in WhatsApp and a popup asked to get access to my contacts. Allowing this access seemed to fix the issue. So for anyone having this issue: you have to allow your phone to access your contacts. Usually this popup asking for access comes automatically when entering the contact list.

— modified on Jun 8, 2018, 8:27:21 PM