Ввиду того, что содержимое посылки не указали, начался таможенный досмотр.

Ввиду того, что means because, since, or more literally in view of the fact that.

It is a fairly formal, written-style connector. In everyday speech, Russians would more often use:

• потому что
• так как
• из-за того, что

So this sentence sounds a bit official or bureaucratic, which fits the customs context well.

In this sentence, ввиду is a fixed preposition/conjunction meaning because of or in view of, so it is written as one word.

Compare:

• ввиду дождя = because of the rain
• ввиду того, что... = because / in view of the fact that...

But в виду as two words usually has a more literal meaning connected with having in view, keeping in mind, or appears in the expression иметь в виду = to mean / to keep in mind.

So here the correct form is definitely ввиду.

This is a complex sentence with a subordinate clause:

• Ввиду того, что содержимое посылки не указали = subordinate clause of reason
• начался таможенный досмотр = main clause

Russian separates this kind of clause with commas.

So:

• the comma before что is part of the fixed structure ввиду того, что
• the second comma marks the end of the subordinate clause before the main clause begins

Structure:

Ввиду того, что ... , начался ...

Russian содержимое is a singular neuter noun meaning the contents or what is inside something.

So even though English often uses a plural noun, Russian treats it as a singular idea:

• содержимое посылки = the contents of the package

This is normal. Russian is focusing on the package’s content as a whole, not on separate individual items.

Because содержимое usually takes the genitive to show contents of what.

So:

• содержимое чего? → посылки

That is why you get:

• содержимое посылки = the contents of the package

This is a very common pattern in Russian:

• цвет дома = the color of the house
• начало фильма = the beginning of the film
• содержимое коробки = the contents of the box

This is a very common Russian pattern called an indefinite-personal construction.

The verb is in the 3rd person plural past:

• указали = they indicated / they specified

But it does not literally mean that a specific group of they is important. It means something like:

• someone didn’t specify it
• it was not specified

Russian often uses this structure when the doer is unknown, unimportant, or obvious from context.

So содержимое посылки не указали is naturally understood as:

• the contents of the package were not specified
• literally: they did not specify the contents of the package

Yes, absolutely.

Both are possible:

• содержимое посылки не указали
• содержимое посылки не было указано

The difference is mostly stylistic:

• не указали sounds natural and standard, with an unnamed human agent in the background
• не было указано is more passive, impersonal, and often even more official or bureaucratic

In administrative or legal contexts, both are common.

Указать is perfective, and указали presents the action as a completed fact: at the relevant moment, the contents were simply not specified.

That fits the context well, because customs is reacting to a completed omission.

If you used the imperfective указывали, it would suggest something more like:

• an ongoing process
• repeated action
• background description

But here the sentence is about one concrete fact, so не указали is the natural choice.

Because the subject is досмотр, and досмотр is a masculine singular noun.

So the verb agrees with it:

• досмотр начался

Compare:

• проверка началась — feminine
• расследование началось — neuter
• досмотр начался — masculine

The adjective also matches:

• таможенный досмотр — masculine singular nominative

It is in the nominative case, because it is the subject of the main clause.

You can see this from the verb agreement:

• начался agrees with досмотр

So the main clause is:

• начался таможенный досмотр
• literally: a customs inspection began

Russian often allows the verb to come before the subject, so even though досмотр comes after начался, it is still the subject.

Досмотр usually suggests a more thorough inspection, search, or check, often in security, border, police, or customs contexts.

So таможенный досмотр is specifically a customs inspection/search.

By contrast, осмотр is more general and can mean:

• inspection
• examination
• viewing
• looking over

For example:

• медицинский осмотр = medical examination
• осмотр квартиры = viewing an apartment

So досмотр is the more precise word here.

Yes, the order can be changed.

The original sentence begins with the reason:

• Ввиду того, что содержимое посылки не указали, начался таможенный досмотр.

This puts emphasis on the cause first, which is very natural in formal written Russian.

You could also say:

• Таможенный досмотр начался ввиду того, что содержимое посылки не указали.

That is also grammatical.

Russian word order is fairly flexible, so the choice often depends on what the speaker wants to emphasize. Here, starting with the reason sounds especially official and document-like.