Learn Hardcore German: Die Stornierung der Buchung ist kostenlos, jedenfalls bis morgen. - The cancellation of the booking is free, in any case until tomorrow.

Because it’s the genitive case. The noun Stornierung (cancellation) can take a genitive complement to say “cancellation of X.” Since Buchung is feminine, its genitive singular article is der. So:

Nominative: die Buchung
Genitive: der Buchung Example: Die Stornierung wessen? – der Buchung.

What genders are “Stornierung” and “Buchung,” and is there a rule?

Both are feminine. A reliable rule: nouns ending in -ung are almost always feminine. Hence:

die Stornierung
die Buchung And in the genitive singular (feminine): der Stornierung, der Buchung.

Could I say “die Stornierung von der Buchung” instead?

That’s not idiomatic here. With abstract nouns like Stornierung, German strongly prefers the genitive over a von-phrase. Use:

Good: die Stornierung der Buchung
Natural alternative: die Buchung stornieren Avoid: die Stornierung von der Buchung (sounds clumsy).

Why is it “kostenlos” and not “kostenlose”?

Because it’s a predicate adjective after sein (“to be”), which doesn’t take an ending:

Predicate: Die Stornierung … ist kostenlos.
Attributive (before a noun) would take an ending: die kostenlose Stornierung.

What’s the nuance among “kostenlos,” “gratis,” “umsonst,” “kostenfrei,” and “gebührenfrei”?

kostenlos/kostenfrei: neutral, standard for “free of charge.” kostenfrei can sound a bit more formal/official.
gratis: also fine; slightly informal or promotional tone.
gebührenfrei: specifically “free of fees,” often in admin/banking contexts.
umsonst: ambiguous; can mean “free of charge” or “in vain.” In contexts like cancellations, prefer kostenlos/kostenfrei to avoid confusion.

What does “jedenfalls” add to the meaning? Could I use “zumindest” or “auf jeden Fall”?

jedenfalls means “in any case/at least,” signaling that the statement is certainly true within a limit: free, at any rate, until tomorrow.
zumindest = “at least,” focusing on a minimal extent: zumindest bis morgen is very close here.
auf jeden Fall = “definitely,” stronger emphasis on certainty; you’d usually say Die Stornierung ist auf jeden Fall kostenlos (bis morgen).
In your sentence, jedenfalls neatly conveys “whatever else may be true, it’s free up to tomorrow.”

Is the comma before “jedenfalls bis morgen” required?

In this shape, yes—it’s a parenthetical afterthought (a “nachgestellte Angabe”), so the comma is correct. Alternatives:

Integrated: Die Stornierung der Buchung ist jedenfalls bis morgen kostenlos. (no comma)
Emphatic with a dash: … ist kostenlos – jedenfalls bis morgen.
Avoid: … ist kostenlos jedenfalls bis morgen. (no separator) — it reads awkwardly.

Does “bis morgen” include tomorrow or not?

It can be ambiguous in deadlines. Many people understand bis morgen as “until the end of tomorrow,” but others may read it as “until tomorrow begins.” If precision matters:

Inclusive: bis einschließlich morgen or bis morgen, 23:59 Uhr
Exclusive (up to the start of tomorrow): bis heute, 24:00 Uhr or bis morgen, 0:00 Uhr (but specify the date to avoid confusion).

Can I move “bis morgen” to the front? How does word order affect emphasis?

Yes. German allows flexible placement of time phrases:

Bis morgen ist die Stornierung der Buchung kostenlos. (emphasizes the time limit)
Die Stornierung der Buchung ist bis morgen kostenlos. (neutral)
Die Stornierung der Buchung ist kostenlos, jedenfalls bis morgen. (adds an afterthought limiting the claim) All obey the verb-second rule in main clauses.

Is “bis zu morgen” possible?

No, not for this meaning. Use bis morgen for “until tomorrow.”
bis zu means “up to” in the sense of a maximum amount/extent (e.g., bis zu drei Tagen = up to three days), not a time point like “tomorrow.”

Why is “morgen” lowercase here?

Lowercase morgen means “tomorrow” (adverb). The uppercase der Morgen is the noun “morning.”

bis morgen = until tomorrow
bis zum Morgen = until the morning (i.e., until the morning part of the day), which is a different meaning.

Could I say “Die Buchung stornieren ist kostenlos”?

Not like that. If you want a verb-noun form, use a proper nominalization or an infinitive clause:

Das Stornieren der Buchung ist kostenlos.
Es ist kostenlos, die Buchung zu stornieren. The bare infinitive as a subject (“Die Buchung stornieren ist …”) is unidiomatic in German.

What’s the difference between “Buchung” and “Reservierung,” and which works with “stornieren”?

Buchung: a booking/purchase (often binding, e.g., paid ticket, hotel booking).
Reservierung: a reservation/hold (can be less binding, like a restaurant table). Both commonly collocate with stornieren:
eine Buchung stornieren
eine Reservierung stornieren
For provider-side cancellations you may also see annullieren (e.g., flights).

Where can “jedenfalls” go in the sentence?

It’s a sentence adverb and can appear:

Midfield: Die Stornierung ist jedenfalls bis morgen kostenlos.
As an afterthought: … ist kostenlos, jedenfalls bis morgen.
Near the start: Jedenfalls ist die Stornierung bis morgen kostenlos.
Placement changes emphasis but not the basic meaning.

Any quick pronunciation tips for tricky parts?

Stornierung: stress on -nie-: [stor-NEE-rung]; the r is tapped/uvular; final -ung like “oong” but with a nasal vowel.
Buchung: ch after u is the voiceless velar fricative , like the “ch” in Scottish “loch.”
jedenfalls: stress on the first syllable: [YEH-den-falz].
morgen: g is like a hard g; the final -en often reduces to a syllabic n.

Why “Die Stornierung … ist …”? Could it be “Eine Stornierung … ist …”?

With die, you’re referring to a specific, known booking’s cancellation (“the cancellation of the booking”). If you mean it generically (any cancellation of this booking), you could also say:

Eine Stornierung der Buchung ist kostenlos …
But in service/terms contexts, the definite form is common because “the booking” is understood from context.