Die Nachzahlung ist nicht plausibel.

Nachzahlung is a noun meaning an additional payment, back payment, or amount that still has to be paid afterward.

It is often used in contexts like:

• utility bills
• rent adjustments
• taxes
• salary corrections

So it usually refers to money that was not fully paid before and is now due.

Nachzahlung is a feminine noun, so its basic article is die.

That is why the sentence starts with:

• die Nachzahlung

In the nominative singular, feminine nouns take die.

It is in the nominative case because it is the subject of the sentence.

In Die Nachzahlung ist nicht plausibel:

• Die Nachzahlung = the subject
• ist = the verb
• nicht plausibel = what is being said about the subject

So the structure is basically:

• The additional payment
  • is
    • not plausible

German main clauses usually put the finite verb in the second position.

So the sentence is arranged like this:

• Die Nachzahlung = position 1
• ist = position 2
• nicht plausibel = the rest

This is standard German word order for a simple statement.

Because nicht is negating the adjective plausibel.

The sentence is saying that the additional payment is not plausible.

Compare:

• Die Nachzahlung ist plausibel. = The additional payment is plausible.
• Die Nachzahlung ist nicht plausibel. = The additional payment is not plausible.

So nicht goes before the adjective it is negating.

Because plausibel is being used as a predicate adjective after sein.

In German, adjectives used:

• before a noun usually get endings
• after verbs like sein, werden, bleiben do not get endings

So:

• eine plausible Erklärung = adjective before a noun, so it changes
• Die Erklärung ist plausibel = adjective after ist, so no ending

That is why it is simply:

• plausibel

Not always exactly.

German plausibel often means:

• reasonable
• believable
• making sense
• convincing enough logically

In this sentence, nicht plausibel often means something like:

• doesn’t make sense
• doesn’t seem justified
• doesn’t seem believable

So although it looks very similar to English plausible, in real usage it can often feel closer to reasonable or logical.

Yes, you can.

unplausibel means implausible, and it is grammatically correct.

However, nicht plausibel is often more natural in everyday German, especially in practical or administrative situations.

The difference is small:

• nicht plausibel = not plausible
• unplausibel = implausible

The second one can sound slightly more formal, direct, or stronger.

It is perfectly normal German, but it sounds a bit formal or administrative because of the words used, especially Nachzahlung and plausibel.

You might see or hear it in:

• billing disputes
• customer service
• housing or utility discussions
• official letters
• accounting contexts

In casual conversation, someone might also say something more everyday like:

• Das ergibt keinen Sinn.
• Das klingt komisch.
• Das kann nicht stimmen.

A rough pronunciation guide is:

dee NAHKH-tsah-loong ist nikht plow-ZEE-bel

A few helpful notes:

• ch in Nach is the throaty German sound
• z in Zahlung sounds like ts
• ie in Die sounds like English ee
• plausibel is stressed on -si-: plau-SI-bel

The pattern is:

Definite article + noun + form of sein + nicht + adjective

So here:

• Die = the
• Nachzahlung = additional payment / back payment
• ist = is
• nicht = not
• plausibel = plausible / reasonable

This is a very common German sentence pattern, and you can reuse it with many other words, for example:

• Die Erklärung ist nicht logisch.
• Der Preis ist nicht fair.
• Die Rechnung ist nicht korrekt.