Retirar diners en descobert té comissió bancària.

Because the whole action retirar diners en descobert is functioning as the subject of the sentence.

A very literal structure would be:

• Retirar diners en descobert = withdrawing money while overdrawn / withdrawing money into overdraft
• té comissió bancària = has a bank fee

Catalan often uses the infinitive this way, just as English can use withdrawing money or to withdraw money as the subject of a sentence.

Because diners here is being used in a general, non-specific way.

• retirar diners = to withdraw money in general
• retirar els diners = to withdraw the money, meaning specific money already known in the context

So the version without an article is the normal choice when talking about the action in general.

That is just how Catalan works: diners is the normal word for money, and it is grammatically plural.

So you get forms like:

• els diners
• molts diners
• quants diners tens?

Even though English treats money as singular, Catalan uses a plural noun here.

In banking language, en descobert means overdrawn or in overdraft.

It refers to the account situation: there is not enough money in the account, or the withdrawal leaves the account below zero.

A very common related expression is:

• estar en descobert = to be overdrawn

In this sentence, en descobert does not describe diners itself. It describes the financial situation in which the money is being withdrawn.

Té is the 3rd person singular of tenir, meaning has.

In practical or administrative Catalan, especially in notices, price lists, or bank information, té can mean something like:

• has
• comes with
• carries
• incurs

So té comissió bancària means that the operation carries a bank fee.

Also note the accent:

• té = has
• te = tea

This is a concise, notice-like style. In Catalan, especially in administrative or commercial language, the article is often omitted in short statements of conditions or charges.

So:

• té comissió bancària = it carries a bank fee / it is subject to bank charges
• té una comissió bancària = a fuller, more explicit version

Both are understandable, but the version without una sounds more compact and informational.

Bancària means bank-related or bank in the sense of something connected to a bank.

It comes after the noun because that is the usual position for adjectives in Catalan.

So:

• comissió bancària = bank fee

And it agrees with comissió, which is feminine singular:

• comissió = feminine singular
• bancària = feminine singular adjective form

Both are possible, but they belong to slightly different registers.

• retirar diners sounds more formal or administrative
• treure diners sounds more everyday and conversational

In bank language, retirar is very common, so this sentence sounds appropriate for a sign, app, contract, or bank notice.

It is understandable and works well in a bank or notice style, but it is a little compact.

A fuller version might be:

• Retirar diners en descobert té una comissió bancària.
• Si retires diners en descobert, et cobren una comissió bancària.

So the original sentence is natural enough in a practical, informational context, even if everyday spoken Catalan might use a slightly fuller wording.