Habida cuenta de que el pago es fraudulento, actuamos.

Habida cuenta de que is a formal fixed expression meaning something like:

• given that
• considering that
• in view of the fact that
• taking into account that

In this sentence, it introduces the reason or basis for the action:

• Habida cuenta de que el pago es fraudulento, actuamos.
• Given that the payment is fraudulent, we act / we acted.

It is especially common in formal writing, such as legal, administrative, or business Spanish.

Because this expression comes from an older structure in which habida agrees with cuenta, which is a feminine singular noun.

Historically, it is related to the idea of account having been taken. So:

• cuenta = feminine singular
• therefore habida

That said, for modern learners, the most useful thing is to treat habida cuenta de as a set phrase. You do not normally change it.

Because habida cuenta de is a prepositional expression, and de is part of it.

The pattern is:

• habida cuenta de + noun phrase
  • Habida cuenta del problema...
• habida cuenta de que + clause
  • Habida cuenta de que el pago es fraudulento...

So in your sentence, since a full clause follows (el pago es fraudulento), Spanish uses de que.

Not really. It is correct, but it sounds formal, bureaucratic, or legalistic.

In everyday Spanish in Spain, people would more often say:

• Dado que el pago es fraudulento, actuamos.
• Como el pago es fraudulento, actuamos.
• Ya que el pago es fraudulento, actuamos.
• Puesto que el pago es fraudulento, actuamos.
• Teniendo en cuenta que el pago es fraudulento, actuamos.

So yes, native speakers understand it, but in normal conversation it may sound rather stiff.

Because the speaker is presenting the information as a fact or at least as something accepted as true.

Expressions like habida cuenta de que, dado que, and puesto que normally take the indicative when the speaker treats the information as real:

• el pago es fraudulento

Using the subjunctive (sea) would sound unusual here unless the sentence were restructured in a special way to show doubt, distance, or some kind of reported wording.

So the indicative is the natural choice.

It can mean either one, because actuamos is the same form for:

• present: we act
• preterite: we acted

Spanish sometimes has this kind of ambiguity, and context normally clears it up.

For example:

• Habida cuenta de que el pago es fraudulento, actuamos de inmediato.
  This could mean we act immediately or we acted immediately, depending on context.

If a speaker wants to make it clearer, they can add time words or use a different structure:

• Ayer actuamos = clearly past
• Ahora actuamos = clearly present
• Estamos actuando = we are acting
• Actuamos ayer = we acted yesterday

Because the sentence begins with a fairly long introductory phrase:

• Habida cuenta de que el pago es fraudulento, ...

In Spanish, a comma is commonly used after this kind of fronted introductory clause or expression, especially in formal writing. It helps readability and makes the structure clearer.

So the comma here is natural and standard.

Because fraudulento agrees with pago, and pago is a masculine noun.

• el pago → masculine
• therefore fraudulento

If the noun were feminine, the adjective would change:

• la transferencia es fraudulenta

So this is just normal adjective agreement.

Not very usefully. A word-for-word approach can be misleading here because this is a fixed expression, not something learners usually build productively from scratch.

It is much better to learn it as a single chunk:

• habida cuenta de que = given that / considering that

If you try to unpack it too literally, it may sound strange in English and it will not help much with using it naturally in Spanish.

Several alternatives are more common in everyday use. They are similar, but not always identical in tone.

• dado que — formal-neutral, very common in writing
• puesto que — quite common, slightly formal
• ya que — common and natural
• como — very common, especially when the reason comes first
• teniendo en cuenta que — close in meaning to taking into account that
• en vista de que — formal, similar to in view of the fact that

Examples:

• Dado que el pago es fraudulento, actuamos.
• Como el pago es fraudulento, actuamos.
• Ya que el pago es fraudulento, actuamos.

So if your goal is natural everyday Spanish, dado que, ya que, or como are often easier and more idiomatic choices.