Possibly one of a kind, this is a type of Notgeld called Briefmarkengeld - or "stamp money" - which was a type of Notgeld which held intrinsic value when a stamp was placed in the perforated slots. It also served as an advertisement, in this case this was an advertisement for the magazine Westermanns Monatshefte that has been given out by what looks like R. Volgenau's Bookstore in Stendal - which is not listed in any catalog anywhere! There is a version of this same Briefmarkengeld that has a different red printed store in Peine along the bottom which catalogs for 100 Euros (and there are examples of that, at least one or two, that can be found to have existed). But THIS note isn't listed in any catalog, isn't mentioned anywhere, and for all appearances may be the only one ever seen anywhere in the world.
Note: the presence of a stamp is not considered to affect the value of Briefmarkengeld, as any collector could easily insert a nice Germania stamp and it would be indistinguishable, in fact, it's probably better if a stamp hasn't been sitting in it for a hundred years, as the condition could have been affected by that.