Numer licznika, termin płatności i rozbieżność są na fakturze.

Because the subject is a list of three things:

• numer licznika
• termin płatności
• rozbieżność

In Polish, when the subject is plural in meaning, the verb is usually plural too, so we use są = are.

If there were only one item, you would use jest:

• Numer licznika jest na fakturze. = The meter number is on the invoice.

Fakturze is in the locative singular.

The preposition na often means on or on/at in a location sense, and when it expresses location, it takes the locative:

• na fakturze = on the invoice

The base form is faktura. Its locative singular is:

• faktura → na fakturze

So the ending -e here is the normal locative singular ending for many feminine nouns.

This is mostly a matter of Polish usage and collocation.

With documents, pages, labels, screens, and similar surfaces or sources of written information, Polish very often uses na:

• na fakturze = on the invoice
• na liście = on the list
• na stronie = on the page
• na etykiecie = on the label

English often uses on in the same kind of way, so this matches fairly well.
Using w fakturze would usually sound unnatural here.

Because Polish commonly expresses X of Y by putting the second noun into the genitive.

So:

• numer = number
• licznik = meter / counter
• licznika = of the meter / counter

Therefore:

• numer licznika = meter number / counter number

This pattern is extremely common:

• numer telefonu = phone number
• adres e-maila = email address
• koniec dnia = end of the day

So the first noun stays in its main form, and the second noun changes to genitive.

For the same reason as numer licznika: this is another noun + genitive structure.

• termin = deadline / due date / term
• płatność = payment
• płatności = of payment

So:

• termin płatności = payment due date / payment deadline

Again, Polish often uses this structure where English might use either of or a noun used like an adjective.

The main subject words are in the nominative:

• numer
• termin
• rozbieżność

But inside the first two noun phrases, the second nouns are in the genitive:

• numer licznika → numer is nominative, licznika is genitive
• termin płatności → termin is nominative, płatności is genitive

So the whole subject is a coordinated list of three nominative items, even though two of them contain genitive nouns inside them.

It is singular.

The form rozbieżność is singular nominative.
If it were plural, it would be rozbieżności.

In this sentence, the verb is plural not because rozbieżność is plural, but because the whole subject is a list of several items.

Yes. Polish word order is fairly flexible because cases show grammatical relationships.

This sentence could also be written as:

• Na fakturze są numer licznika, termin płatności i rozbieżność.

That version puts more focus on where the items are.
The original version starts with the items themselves, then says where they are.

Both are natural, though the exact emphasis changes.

Because in a simple list, Polish normally does not put a comma before i (and).

So this is standard:

• Numer licznika, termin płatności i rozbieżność...

The commas separate the first items in the list, and i connects the final one.

This is similar to English without the Oxford comma:

• meter number, payment due date and discrepancy

No. Polish does not have articles like English a/an/the.

So:

• Numer licznika can mean the meter number or just meter number
• na fakturze can mean on the invoice or on an invoice

The exact meaning depends on context.
That is normal in Polish, and learners need to get used to understanding definiteness from the situation rather than from an article.

Here are the genders of the main nouns:

• numer — masculine
• licznik — masculine
• termin — masculine
• płatność — feminine
• rozbieżność — feminine
• faktura — feminine

This matters because gender affects adjective endings, past tense forms, and some case endings.

For example:

• ta faktura = this invoice
• ta rozbieżność = this discrepancy
• ten numer = this number
• ten termin = this deadline

In standard Polish, no. You normally keep the present-tense form of być here.

So the correct sentence is:

• Numer licznika, termin płatności i rozbieżność są na fakturze.

Leaving out są would sound incomplete or unnatural in ordinary standard Polish.

Polish sometimes omits verbs in very informal notes, headlines, or special stylistic contexts, but not in a normal full sentence like this.

Not always. Licznik can mean different kinds of counter or meter, depending on context.

Common meanings include:

• a utility meter, such as an electricity or gas meter
• a counter device
• a tally or measuring counter

So numer licznika is often meter number, especially in billing or utility contexts.
The exact meaning depends on the kind of document being discussed.

Yes, especially in an administrative, billing, or customer-service context. It sounds like something you might see or hear when discussing what information appears on an invoice.

It is slightly formal or informational rather than conversational, but it is completely natural Polish.