O código postal estava errado; daí o atraso.

Here daí means hence, therefore, that’s why, or as a result.

So daí o atraso means something like:

• hence the delay
• therefore, the delay
• that’s why there was a delay

This use of daí is quite common in Portuguese and is a compact way of expressing a consequence.

It is an elliptical expression, meaning some words are left out because they are understood from the context.

Daí o atraso is short for something like:

• Daí resultou o atraso
• Daí veio o atraso
• Daí se explica o atraso

In English, this works a lot like hence the delay, where English also leaves out the verb.

So even though there is no explicit verb, the meaning is perfectly natural.

Estava errado is the natural choice here because it describes a state or condition of the postal code in that situation.

• estar errado = to be wrong / incorrect in a particular case
• ser errado = to be wrong in a more essential, general, or moral sense

With factual mistakes such as an address, number, answer, or postal code, Portuguese normally uses estar:

• O número estava errado.
• A morada estava errada.
• O nome estava errado.

Using era errado here would sound unusual.

Because it agrees with o código postal, which is:

• masculine: o
• singular: one postal code

So the adjective must match:

• o código postal estava errado
• if it were feminine: a morada estava errada
• if plural masculine: os códigos postais estavam errados

Agreement is very important in Portuguese.

The semicolon links two closely related parts:

• O código postal estava errado
• daí o atraso

It shows that the second part is a direct consequence of the first.

You could also find:

• O código postal estava errado. Daí o atraso.
• O código postal estava errado, daí o atraso.

But the semicolon gives a neat, slightly more formal written style. It is especially suitable because the second part is short and strongly connected to the first.

Yes, but the structure changes a little.

You can say:

• O código postal estava errado; por isso houve atraso.
• O código postal estava errado; por isso se atrasou.
• O código postal estava errado; por isso é que houve atraso.

But daí o atraso is shorter and more compact.

A useful distinction:

• daí often appears in concise, written cause-result phrasing
• por isso is very common and often feels a bit more explicit in everyday speech

So both work, but daí o atraso is a very natural fixed-type expression.

Yes. In European Portuguese, daí is common both in its literal meaning and in this consequence meaning.

It can mean:

1. from there

   • Saí de Lisboa e daí fui para Coimbra.

2. hence / therefore

   • Estava doente; daí a ausência.

In your sentence it is the second meaning.

This use is normal and idiomatic in Portugal, especially in writing and in slightly more concise speech.

Portuguese often uses the definite article where English may or may not.

Here o atraso means the delay. It refers to the delay that resulted from the wrong postal code.

This is very natural in Portuguese:

• daí o problema
• daí a confusão
• daí o atraso

Leaving out the article would sound less natural here.

Normally, no. Foi errado does not sound natural for this meaning.

For mistakes in information, Portuguese usually says:

• estava errado = was wrong / was incorrect

Foi errado can sometimes appear in other contexts, but not naturally for a postal code containing the wrong information.

So the best version here is:

• O código postal estava errado.

Both can work, but errado is more common and more everyday.

• errado = wrong
• incorreto = incorrect

So you could say:

• O código postal estava errado.
• O código postal estava incorreto.

The second sounds a bit more formal or technical. In ordinary usage, errado is usually the more natural choice.

It sounds mostly neutral to slightly formal, especially because of the semicolon and the concise expression daí o atraso.

More neutral/everyday alternatives might be:

• O código postal estava errado, por isso houve atraso.
• O código postal estava errado, por isso é que se atrasou.

Your original sentence is perfectly natural, but it has a slightly tighter, more written feel.

Yes. In Portugal, código postal is the standard term for postal code.

That is the normal expression you should learn and use.

Partly, yes.

A close English equivalent is:

• The postal code was wrong; hence the delay.

That is quite close in structure and style.

A more everyday English version would be:

• The postal code was wrong, so there was a delay.
• The postal code was wrong; that’s why there was a delay.

So the Portuguese sentence maps especially well to the English pattern hence the delay.