Mia monujo estas malplena, do mi pagos per karto.

Yes. Monujo is a normal Esperanto word for a wallet or purse.

It is built from:

• mono = money
• -ujo = a container or holder for something

So monujo literally means money-container or money-holder. Esperanto often builds words this way.

Because mia monujo is the subject of the sentence: it is the thing that is empty.

In Esperanto:

• mia = my
• monujo = wallet
• mia monujo = my wallet

There is no -n here because the accusative -n is mainly used for a direct object. This phrase is not a direct object.

Also, possessive words like mia behave like adjectives, so they can agree if needed:

• mia monujo = my wallet
• miaj monujoj = my wallets
• mian monujon = my wallet as a direct object

But in this sentence, simple mia monujo is correct.

Malplena is made from:

• plena = full
• mal- = the opposite

So:

• plena = full
• malplena = empty

This is a very common Esperanto pattern. The prefix mal- often creates the opposite meaning:

• bona = good → malbona = bad
• granda = big → malgranda = small
• plena = full → malplena = empty

The ending -a shows that malplena is an adjective, describing monujo.

Because it is a predicate adjective, not a direct object.

In Mia monujo estas malplena:

• mia monujo is the subject
• estas links the subject to its description
• malplena describes the subject

Predicate adjectives agree with the subject in number and case. Since monujo is singular and has no -n, the adjective also stays singular with no -n:

• La monujo estas malplena.
• La monujoj estas malplenaj.

Because the sentence talks about two different times:

• Mia monujo estas malplena = my wallet is empty now
• do mi pagos per karto = so I will pay by card

Esperanto uses the tense that matches each action or state:

• -as = present
• -is = past
• -os = future

So the wallet’s condition is present, but the payment happens afterward.

Because Esperanto verb endings are very regular.

From pagi = to pay:

• pagas = pay / am paying
• pagis = paid
• pagos = will pay
• pagus = would pay
• pagu = pay! / let ... pay
• pagi = to pay

So mi pagos clearly means I will pay.

Do means so, therefore, or thus.

It shows that the second clause is the result of the first:

• Mia monujo estas malplena = my wallet is empty
• do mi pagos per karto = so I will pay by card

It is a very common word for connecting cause and result.

Because per means by means of, using, or through. It marks the method or instrument.

So:

• Mi pagos per karto = I will pay by card / using a card

By contrast, kun means with in the sense of together with or accompanied by:

• Mi venis kun amiko = I came with a friend

A native English speaker may want to use kun because English says with a card, but Esperanto normally uses per for the means used to do something.

Because it comes after the preposition per.

Normally, nouns after prepositions do not take the accusative -n:

• per karto
• kun amiko
• en la domo

Here karto is not the direct object of pagos. It is part of the prepositional phrase per karto, which tells you how the person will pay.

No. Esperanto has only one article: la.

It does not have separate words for a or an.

So:

• monujo can mean a wallet or just wallet, depending on context
• karto can mean a card

Also, possessives like mia already make the noun specific, so mia monujo is natural without la.

That is why:

• mia monujo = my wallet
• per karto = by card / with a card

Yes, Esperanto word order is fairly flexible, but this sentence uses the most natural, straightforward order.

Standard order here is:

• Mia monujo = subject
• estas = verb
• malplena = description
• do mi pagos = result clause
• per karto = method

You could sometimes move parts around for emphasis, but this version is the clearest and most neutral for learners.