Do they provide an invoice that fulfils the accounting requirements of your country? I suspect not, so you wouldn’t be able to deduct it.
Any links to back that up?
What I find around the net seems to point in the opposite direction. For example the German "Eigenbeleg":
https://de.wikipedia.org/wiki/Eigenbeleg
The Wikipedia page says that to deduct expenses from earnings, the expense has to be "belegt" which means "documented". But it seems the documentation does not have to be done by the seller. It seems it can also also be done by the buyer.
While it might be possible to use them this way they might be scrutinized and the additional work of justifying them might not be worth using a service that doesn't provide receipts.
Also, there is this section:
> Soll die Ausgabe vom Finanzamt anerkannt werden, muss dies ein Ausnahmefall bleiben.
Meaning, roughly "Even if accepted by the authorities, it is to be treated as an exception"
So i assume that they would not be a fan of you trying to use this too liberally within your accounting.