Alles is klaar voor de herplaatsing, behalve dat het chipnummer ontbreekt.

Alles means everything, and in Dutch it is treated as grammatically singular. That is why it takes is.

• Alles is klaar = Everything is ready
• not Alles zijn klaar

Compare that with alle:

• alle documenten zijn klaar = all documents are ready

So alles = everything and usually takes singular verbs, while alle + plural noun takes a plural verb.

Klaar voor means ready for.

So:

• klaar = ready
• voor = for

Together:

• Alles is klaar voor de herplaatsing = Everything is ready for the rehoming / relocation

Be careful: voor can also mean before in other contexts, but not here. In this sentence, it is part of the expression klaar voor.

Literally, herplaatsing is built like this:

• her- = re-, again
• plaats = place
• -ing = a noun ending, like -ing in English

So herplaatsing is something like re-placement, relocation, or rehoming, depending on context.

In animal or administrative contexts, herplaatsing often means rehoming or placing somewhere else again.

Herplaatsing is a de-word, so it takes de.

A useful pattern is that many nouns ending in -ing are de-words:

• de herplaatsing
• de opleiding
• de vergunning

So here, de herplaatsing is the correct form.

Behalve dat means except that.

It introduces an exception to what was just said:

• Alles is klaar voor de herplaatsing = everything is ready for the rehoming
• behalve dat het chipnummer ontbreekt = except that the chip number is missing

So the sentence means that everything is ready, with one exception.

Because behalve dat introduces a whole clause, not just a noun.

Compare:

• behalve het chipnummer = except the chip number
• behalve dat het chipnummer ontbreekt = except that the chip number is missing

In the sentence you gave, what follows is a full clause:

• het chipnummer ontbreekt

That is why dat is used.

Because after dat, Dutch normally uses subordinate clause word order, where the finite verb goes to the end.

So:

• main clause: Het chipnummer ontbreekt
• subordinate clause: dat het chipnummer ontbreekt

This is a very common Dutch pattern:

• Ik weet dat hij komt
• Ze zegt dat het moeilijk is
• behalve dat het chipnummer ontbreekt

So the final position of ontbreekt is normal.

Ontbreekt is the singular form of ontbreken, which means to be missing, to be absent, or to be lacking.

Here:

• het chipnummer ontbreekt = the chip number is missing

A very useful difference:

• Het chipnummer ontbreekt = the chip number is not there
• Wij missen het chipnummer = we are missing the chip number / we do not have it

So ontbreken focuses on the thing that is absent.

Because chipnummer is a het-word.

A helpful rule for compounds in Dutch is that the gender usually comes from the last part of the compound. The last part here is nummer, and nummer is a het-word:

• het nummer
• therefore het chipnummer

So even though chip is the first part, the important part for the article is nummer.

Because Dutch usually writes compound nouns as one word.

So:

• chip
  • nummer → chipnummer

This is very normal in Dutch:

• huisdeur = house door / front door
• telefoonnummer = telephone number
• dierenartspraktijk = veterinary practice

English often uses spaces where Dutch prefers one long compound word.

Yes, you could, and it may sound a little more direct in everyday speech:

• Alles is klaar voor de herplaatsing, maar het chipnummer ontbreekt.

That means nearly the same thing: Everything is ready for the rehoming, but the chip number is missing.

The version with behalve dat is slightly more like everything is ready, except that...
The version with maar is slightly more straightforward: everything is ready, but...

Both are natural, though behalve dat emphasizes the idea of a single exception.

It has two parts:

1. Alles is klaar voor de herplaatsing

   • Alles = subject
   • is = verb
   • klaar = predicate adjective
   • voor de herplaatsing = prepositional phrase

2. behalve dat het chipnummer ontbreekt

   • behalve dat = except that
   • het chipnummer = subject of the subordinate clause
   • ontbreekt = verb

So the overall structure is:

• statement: everything is ready
• exception: the chip number is missing