Nach der Rechnungskorrektur sinkt der Abschlag; die Zahlungsfrist endet am Freitag.

Nach means after here, and it is a preposition that takes the dative case. That is why you get der Rechnungskorrektur, not die Rechnungskorrektur.

• nach + dative
• die Rechnungskorrektur → der Rechnungskorrektur in the dative singular

So Nach der Rechnungskorrektur means After the invoice correction or After the correction of the invoice.

Because Rechnungskorrektur is a feminine noun (die Rechnungskorrektur), and after nach you need the dative.

For feminine singular nouns:

• nominative: die Rechnungskorrektur
• dative: der Rechnungskorrektur

So the form changes because of the case, not because the meaning changes.

German main clauses follow the V2 rule: the finite verb must be in the second position.

Here, the first position is taken by the whole phrase:

• Nach der Rechnungskorrektur = position 1
• sinkt = position 2
• der Abschlag = then comes the subject

So German says:

• Nach der Rechnungskorrektur sinkt der Abschlag.

Even though the subject comes after the verb, it is still the subject.

The subject is der Abschlag.

You can tell because:

• sinkt is singular
• der Abschlag is nominative singular masculine

So the structure is:

• Nach der Rechnungskorrektur = adverbial phrase
• sinkt = verb
• der Abschlag = subject

This is very common in German when something other than the subject comes first.

Abschlag can mean different things depending on context, so learners often pause here.

Common meanings include:

• discount / reduction
• down payment / installment / advance payment
• in some contexts, a deduction

In a billing or payment context like this one, it often refers to an installment, advance payment, or reduced amount due. The exact best English word depends on the wider context.

So the important thing for grammar is:

• der Abschlag is a masculine noun
• here it is the thing that goes down / decreases

The semicolon links two closely related independent clauses:

• Nach der Rechnungskorrektur sinkt der Abschlag
• die Zahlungsfrist endet am Freitag

A semicolon is stronger than a comma and weaker than a full stop. It shows the two facts belong together.

You could also write:

• Nach der Rechnungskorrektur sinkt der Abschlag. Die Zahlungsfrist endet am Freitag.

Or with und, depending on style:

• Nach der Rechnungskorrektur sinkt der Abschlag, und die Zahlungsfrist endet am Freitag.

The semicolon is just a punctuation choice.

Die Zahlungsfrist means payment deadline, payment period, or time allowed for payment.

It is made from:

• Zahlung = payment
• Frist = deadline / time limit

It is a feminine noun:

• nominative: die Zahlungsfrist

In the second clause, it is the subject:

• die Zahlungsfrist endet am Freitag

In German, days of the week often appear with am when you mean on a certain day.

• am = contraction of an dem
• am Freitag = on Friday

So:

• Die Zahlungsfrist endet am Freitag = The payment deadline ends on Friday

Without am, Freitag would not sound correct in this sentence.

Actually, endet is not at the end of the clause in the German grammar sense; it is in the normal second position of the main clause.

The clause is:

• die Zahlungsfrist = position 1
• endet = position 2
• am Freitag = rest of the clause

German main clauses usually place the finite verb second, and that is exactly what happens here.

Yes. That is also correct.

Compare:

• Nach der Rechnungskorrektur sinkt der Abschlag.
• Der Abschlag sinkt nach der Rechnungskorrektur.

Both mean the same thing. The difference is emphasis:

• starting with Nach der Rechnungskorrektur emphasizes the timing or condition
• starting with Der Abschlag emphasizes the subject

German word order is flexible in this way, as long as the verb stays in second position in a main clause.

Yes. Rechnungskorrektur is a compound noun:

• Rechnung = invoice / bill
• Korrektur = correction

Together:

• Rechnungskorrektur = invoice correction / correction of the invoice

German uses compound nouns very often, and the last part determines the grammatical gender:

• die Korrektur
• therefore die Rechnungskorrektur

German usually uses articles more regularly than English. In a sentence like this, the nouns appear with their definite articles because they refer to specific things already known in the context:

• der Abschlag
• die Zahlungsfrist

English might sometimes omit an article or phrase things differently, but in German this is very normal and natural.

Yes. Sinken is an intransitive verb, meaning the thing itself goes down or decreases.

• Der Abschlag sinkt. = The amount/installment decreases.

Compare that with a transitive verb like senken:

• Die Firma senkt den Abschlag. = The company lowers the installment/amount.

So:

• sinken = to sink / decrease
• senken = to lower something

That contrast is very common in German.