Post kiam mi pagis, mi ricevis kvitancon.

Post by itself is a preposition and is normally followed by a noun or noun phrase, such as post la pago (after the payment) or post la kunveno (after the meeting).

In this sentence, what follows is a whole clause: mi pagis (I paid). To connect after to a full clause, Esperanto uses post kiam:

• post la pago = after the payment
• post kiam mi pagis = after I paid

So kiam is needed because the idea after post is expressed as a clause, not a noun.

Esperanto verbs have very regular endings:

• -as = present
• -is = past
• -os = future
• -us = conditional
• -u = imperative / volitive

So pagis means paid.

Since the sentence talks about two actions in the past—

1. mi pagis = I paid
2. mi ricevis kvitancon = I received a receipt

—both verbs appear in the past tense: pagis and ricevis.

The -n ending marks the direct object in Esperanto.

Here, kvitancon is the thing that was received. Ask yourself: I received what? The answer is a receipt, so kvitancon is the direct object.

• mi ricevis kvitancon = I received a receipt

Without the -n, the noun would not be marked as the object.

The base form is kvitanco, which means receipt.

Breaking it down:

• kvitanc-o = receipt
• kvitanc-on = receipt as a direct object

So the dictionary form is kvitanco, and the sentence uses kvitancon because it is the object of ricevis.

Esperanto normally states the subject of each clause clearly, even when English might sometimes leave it implied.

So:

• Post kiam mi pagis, mi ricevis kvitancon.

literally has:

• After I paid, I received a receipt.

The second mi is not optional in normal Esperanto here, because mi ricevis is a new clause and needs its own subject.

Yes. That word order is also correct.

Esperanto word order is fairly flexible, as long as the grammar is clear. These mean the same thing:

• Post kiam mi pagis, mi ricevis kvitancon.
• Mi ricevis kvitancon post kiam mi pagis.

The version with Post kiam... at the beginning puts the time relationship first, a bit like English After I paid, I received a receipt.

The comma separates the introductory subordinate clause from the main clause.

• Post kiam mi pagis = subordinate time clause
• mi ricevis kvitancon = main clause

Using a comma here is standard and helps readability. It works much like English punctuation in a sentence such as:

• After I paid, I received a receipt.

Not always. It depends on what comes next.

Use post alone before a noun:

• post la pago = after the payment
• post tio = after that

Use post kiam before a clause:

• post kiam mi pagis = after I paid
• post kiam li alvenis = after he arrived

So in this sentence, post kiam is the natural choice because the next part is a full clause: mi pagis.

Yes, in many contexts ricevi can correspond to English receive or get.

• mi ricevis kvitancon = I received a receipt
• also naturally: I got a receipt

Received is a bit more formal, while got is more everyday English. The Esperanto verb itself is neutral.

Yes. Pagi can be used without explicitly naming the object if the meaning is already clear from context.

So mi pagis simply means I paid.

If you want to be more specific, you can add an object:

• Mi pagis la fakturon. = I paid the bill.
• Mi pagis la prezon. = I paid the price.

But in the sentence given, just mi pagis is perfectly normal because the important point is the sequence: first the payment, then the receipt.