0 Euro banknotes

There are many of these so-called banknotes with a value of 0 Euro.

I assume that they cannot be called banknotes, but someone affirms that instead, they are legal tender banknotes.

Which is the correct answer?

They are made by different private institues but not by any governement so no legal tender as a governement will not realease a note with a face value of 0 because to be legal tender it should be superior to 0.

N#217150

Something like this - ATM test note

‘0 Euro’ items are exonumia.

Aidan.