Regenerating the same product does not use up my allowance

Correct, and deliberate. Generated content is cached against a fingerprint of the product's own data. If nothing about the product has changed, asking again returns the stored text rather than generating it afresh, so it costs nothing from your allowance. Change the product, or change the length, tone or language you are asking for, and the fingerprint changes, so the app generates properly instead of serving stale text.

One exception is worth knowing: if a previous attempt fell back to placeholder text because the generation itself failed, that fallback is never treated as a cache hit. The next attempt genuinely regenerates.