The apostille went on a copy when it was needed on the original
A client was assembling a family reunification file for Germany. She took her birth certificate to a notary, made a notarised copy, had that copy apostilled at the Ministry of Justice, and then ordered a German translation from us. Three weeks later the German authority returned the document with a brief note: the apostille has to be on the birth certificate itself, not on a copy. The whole path had to be walked again — a month lost, a second state fee for the apostille, and another paid translation, because the document is translated together with the new stamp.
Why an apostille can go in three different places
An apostille certifies the authenticity of a signature and seal on one specific sheet of paper. Your file may contain several such "sheets", and they are not equivalent. The first is the document issued by a state body: a civil-registry certificate, a police record, a diploma. The second is a notarised copy of that document. The third is a notarised translation. Each of these is apostilled separately and by a different authority: civil-registry acts by the regional registry office, notarial documents (copies and translations) by the territorial branch of the Ministry of Justice.
The client chose to apostille the copy because that was recommended "for speed": a copy is easier to obtain than a fresh certified duplicate. But the German request read "apostillierte Geburtsurkunde" — an apostilled birth certificate, meaning the stamp on the civil-registry document itself. The difference is one word, but in practice it is two different authorities and two different procedures.
How to read the requirement correctly
Before you apostille anything, get the receiving organisation's requirement in writing and read it literally. "Apostille on the original", "on the document issued by the civil-registry office", "on the original document" — a copy will not do. "Apostilled copy", "notarielle Kopie mit Apostille", "apostilled certified copy" — the opposite: the original does not need an apostille, you work with the copy. If the wording is vague ("document with apostille"), ask the sender what exactly they mean.
When there is no one to ask, it is safer to apostille the original. That document is accepted almost everywhere, whereas an apostilled copy is not accepted by every authority, because for them it is a "copy of a copy": a notary now stands between the source act and the apostille.
One last point: the apostille always goes on before translation. The apostille stamp is part of the document; its text is translated too and is included in the notarised translation. Translate before the apostille is added and the translation has to be redone.