Mi pagas kotizon sed ne monpunon.

The -n ending marks the direct object in Esperanto: the thing the action is done to.

• Mi pagas kotizon = I pay a fee
• Mi pagas monpunon = I pay a fine

Here, the verb pagas is acting on kotizo and monpuno, so both take -n.

This is one of the most important endings in Esperanto. Even if the word order changes, the -n still shows which noun is the object.

Pagas is the present tense form of the verb pagi.

Esperanto verb endings are very regular:

• -as = present
  
  • mi pagas = I pay / I am paying
• -is = past
  
  • mi pagis = I paid
• -os = future
  
  • mi pagos = I will pay
• -us = conditional
  
  • mi pagus = I would pay
• -u = command / wish
  
  • pagu = pay!

So Mi pagas kotizon sed ne monpunon is in the present tense because pagas ends in -as.

Esperanto does not have an indefinite article like English a/an.

So:

• kotizo can mean a fee or just fee, depending on context
• monpuno can mean a fine

Esperanto does have a definite article: la = the

So if you wanted to say the fee, you could say:

• Mi pagas la kotizon sed ne la monpunon.

Without la, the nouns are indefinite or general.

Sed means but.

It shows a contrast:

• Mi pagas kotizon sed ne monpunon. = I pay a fee, but not a fine.

If you used kaj (and), the meaning would be different:

• Mi pagas kotizon kaj monpunon. = I pay a fee and a fine.

So sed is the right conjunction because the sentence contrasts one thing with another.

This is a shortened form that avoids repeating what is already clear.

Full version:

• Mi pagas kotizon sed mi ne pagas monpunon.

Shorter version:

• Mi pagas kotizon sed ne monpunon.

In the shorter sentence, Esperanto leaves out the repeated mi pagas because it is understood from the first half. English does this too sometimes:

• I pay a fee, but not a fine.

So ne monpunon means something like not a fine after the already understood I pay.

Usually, yes: ne comes before the part being negated.

In this sentence:

• sed ne monpunon

the ne negates monpunon, meaning not a fine.

Compare:

• Mi ne pagas kotizon. = I do not pay a fee.
  Here ne negates the verb phrase.
• Mi pagas ne kotizon sed monpunon. = I pay not a fee but a fine.
  Here ne negates kotizon.

So placement matters. In your sentence, ne is specifically rejecting monpunon as the thing being paid.

They are both payments, but they are different kinds of payments.

• kotizo = a fee, due, or membership payment
• monpuno = a fine, a money penalty

So:

• kotizo is usually a normal required payment
• monpuno is a punishment involving money

Also, monpuno is a compound word:

• mono = money
• puno = punishment

So monpuno literally means something like money-punishment.

Yes, Esperanto word order is fairly flexible, because endings show the grammatical roles.

The normal order here is:

• Mi pagas kotizon sed ne monpunon.

But other orders are possible for emphasis, for example:

• Kotizon mi pagas, sed ne monpunon.

That gives extra emphasis to kotizon.

Still, for learners, the basic subject–verb–object order is usually the safest and most natural choice.

Often, yes.

Many writers would write:

• Mi pagas kotizon, sed ne monpunon.

The comma before sed is common because sed connects two contrasting parts.

However, punctuation in Esperanto can be a bit flexible, especially in short sentences. So you may see both versions. If you want to write in a clear, standard way, using the comma before sed is a good idea.

Usually, no.

Esperanto verbs do not change depending on the subject:

• mi pagas
• vi pagas
• li pagas
• ili pagas

Because the verb form pagas does not tell you who is doing the action, the subject pronoun is normally needed unless the context makes it completely obvious.

So:

• Mi pagas kotizon sed ne monpunon. = normal
• Pagas kotizon sed ne monpunon. = possible only in special contexts, but not the normal choice for learners

For clear everyday Esperanto, keep mi.