Greška je sada ispravljena.

• greška = mistake, error
• je = is
• sada = now
• ispravljena = corrected

So the sentence literally looks like Mistake is now corrected, but in natural English it is usually The mistake has now been corrected or The mistake is now corrected.

This is a passive construction.

• je is the present tense of biti = to be
• ispravljena is the passive participle of ispraviti = to correct

Together they mean something like is corrected / has been corrected, depending on context.

So:

• Greška je ispravljena = The mistake is corrected / has been corrected

Croatian often builds the passive this way:
biti + passive participle

Because ispravljena has to agree with greška.

The noun greška is:

• feminine
• singular

So the participle must also be:

• feminine
• singular

That gives ispravljena.

Compare:

• Problem je ispravljen. = The problem has been corrected.
  
  • problem is masculine, so ispravljen
• Pismo je ispravljeno. = The letter/document has been corrected.
  
  • pismo is neuter, so ispravljeno
• Greška je ispravljena. = The mistake has been corrected.
  
  • greška is feminine, so ispravljena

Grammatically, je is present tense, but the whole sentence usually describes a completed correction with a present result.

That is why English may translate it in two ways:

• The mistake is now corrected
• The mistake has now been corrected

In many contexts, the second English translation sounds more natural because the correction has already happened.

Sada means now, and Croatian word order is fairly flexible. Putting sada there is completely normal.

These are all possible, with slightly different emphasis:

• Greška je sada ispravljena.
• Sada je greška ispravljena.
• Greška je ispravljena sada. — possible, but less neutral
• Greška je ispravljena. — without sada

The original sentence sounds natural and neutral.

Yes. Sad and sada both mean now.

• sada is a bit more neutral or slightly more formal
• sad is very common in everyday speech

So you can say:

• Greška je sada ispravljena.
• Greška je sad ispravljena.

Both are correct.

It comes from the verb ispraviti, which means to correct, to fix, or to set right, depending on context.

Here:

• ispraviti grešku = to correct a mistake

The form ispravljena is the passive participle built from ispraviti.

This verb is also perfective, which fits the idea that the correction has been completed.

Because with errors, mistakes, spelling, grammar, facts, data, Croatian very often uses ispraviti.

Examples:

• ispraviti grešku = correct a mistake
• ispraviti pravopisnu grešku = correct a spelling mistake
• ispraviti tekst = correct/edit a text

Popraviti usually means repair or fix something that is broken or not functioning well:

• popraviti auto = repair a car
• popraviti računalo = fix a computer

Sometimes popraviti can be used more broadly, but for greška, ispraviti is the most natural choice.

Yes, it is a passive sentence. The doer of the action is not mentioned.

Active versions could be:

• Sada su ispravili grešku. = They have now corrected the mistake.
• Urednik je sada ispravio grešku. = The editor has now corrected the mistake.

Croatian often uses the passive when the important thing is the result, not who did it.

Yes, absolutely. In fact, that is very common.

Greška je sada ispravljena focuses on the result:

• the mistake existed before
• now it no longer does

If you want to add the agent, Croatian can do it, but it often sounds more natural to switch to an active sentence rather than adding a by-phrase.

Less common passive-style option:

• Greška je sada ispravljena od strane urednika.

More natural active option:

• Urednik je sada ispravio grešku.

Yes. It sounds natural, especially in formal, technical, written, or customer-service contexts.

For example:

• after fixing a typo
• after correcting a bug or error
• in a support message
• in an edited document

In casual speech, people might also say:

• Ispravili smo grešku. = We corrected the mistake.
• Greška je ispravljena. = The mistake has been corrected.
• Sad je sve u redu. = Now everything is fine.

Yes. Greška is a regular feminine noun.

That is why you get:

• ta greška = that mistake
• ova greška = this mistake
• greška je ispravljena = the mistake has been corrected

Its ending -a is a strong clue that it is feminine, and in this case that clue is correct.

Yes. Croatian does not always separate those two meanings as sharply as English does.

Depending on context, Greška je sada ispravljena can emphasize:

• the current state: the mistake is now corrected
• the completed action with present relevance: the mistake has now been corrected

In many real situations, both ideas are present at once, so English translation depends on what sounds most natural in context.