Keep a price adjective attached to what it describes
Kostenlos teilnehmen, freiwillig etwas kaufen
Distinguish absence of a charge from a low charge, and participation from a separate optional purchase.
Kostenlos, kostenfrei and gratis can describe participation without payment here. Kostenarm means involving little cost, which is a different claim. The optional four-euro package is not a hidden requirement: own materials suffice and the package contains nothing essential for participation. Interpret the price adjective with its object and the explicit conditions, rather than extending it to everything offered on site.
Die Teilnahme ist kostenlos.
Participation is free of charge.
Eigenes Material reicht für die Teilnahme aus.
Own materials suffice for participation.
Das zusätzliche Paket ist freiwillig erhältlich.
The additional package is available as an optional purchase.
Kostenarm bezeichnet nicht eindeutig einen Preis von null Euro.
Low-cost does not unambiguously specify a price of zero euros.
Der Bezugsbereich des Adjektivs muss erkennbar bleiben.
What the adjective refers to must remain identifiable.
Ein freiwilliger Kauf ist keine Zugangsvoraussetzung.
An optional purchase is not an entry requirement.
Kostenlos, kostenfrei and gratis can describe participation without payment here. Kostenarm means involving little cost, which is a different claim. The optional four-euro package is not a hidden requirement: own materials suffice and the package contains nothing essential for participation. Interpret the price adjective with its object and the explicit conditions, rather than extending it to everything offered on site.
Distinguish absence of a charge from a low charge, and participation from a separate optional purchase.
Do not change zero participation cost into merely low cost or present the optional purchase as compulsory.
Word formation supplies clues, not a substitute for context. In these uses -los/-frei indicate absence of a charge, while -arm indicates a small amount. Establish exactly which service or object the adjective modifies. A statement about participation does not automatically price a separately offered optional item.
Write a 250–300-word German explanation for the library newsletter team. Compare kostenlos and kostenarm, identify why the shortened advert could mislead and propose a precise version distinguishing participation, own materials and the optional package. Do not make claims about general advertising law.