De webwinkel bevestigde dat het pakket was zoekgeraakt.

Yes. Webwinkel is a very normal Dutch word for an online store / webshop.

It is a compound:

• web = web / internet
• winkel = shop / store

So literally it means web store. You will also see webshop, but webwinkel is standard Dutch.

Dutch nouns take either de or het as their definite article.

• de webwinkel → webwinkel is a de-word
• het pakket → pakket is a het-word

For many nouns, you simply have to learn the article with the noun. English speakers often want a rule, but in many cases it is just vocabulary you memorize.

Bevestigde is the simple past of bevestigen.

• infinitive: bevestigen = to confirm
• simple past singular: bevestigde = confirmed

So De webwinkel bevestigde ... means The online store confirmed ...

This is a regular weak verb, which is why the past tense ends in -de.

Dat introduces a subordinate clause, just like English that in:

• The online store confirmed that the package had gotten lost.

So:

• De webwinkel bevestigde = The online store confirmed
• dat het pakket was zoekgeraakt = that the package had gotten lost

After verbs like zeggen, denken, weten, merken, bevestigen, Dutch often uses dat to introduce what was said, thought, known, noticed, or confirmed.

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

Main clause order:

• Het pakket was zoekgeraakt.

Subordinate clause after dat:

• ... dat het pakket was zoekgeraakt.

So the subject het pakket comes before the verb cluster, and the verbs move to the end of that clause.

Zoekgeraakt is the past participle of zoekraken.

• zoek = lost / missing
• raken = to get / become

So zoekraken literally means something like to become lost or to get lost.

Examples:

• Het pakket raakte zoek. = The package got lost.
• Het pakket is zoekgeraakt. = The package has gotten lost.
• Het pakket was zoekgeraakt. = The package had gotten lost.

This is a very useful Dutch way to talk about something going missing.

Because zoekraken behaves like a separable verb.

In Dutch, separable verbs often:

• split in some finite forms
• stay together in the infinitive and past participle

For example:

• infinitive: zoekraken
• simple past: raakte zoek
• past participle: zoekgeraakt

So:

• Het pakket raakte zoek. but
• Het pakket is zoekgeraakt.

That pattern is very common in Dutch separable verbs.

Because the sentence describes two past events:

1. the package got lost
2. later, the web store confirmed that fact

Dutch uses the past perfect / pluperfect for the earlier past event:

• bevestigde = confirmed
• was zoekgeraakt = had gotten lost

So was zoekgeraakt shows that the losing happened before the confirming.

If you said dat het pakket zoekraakte or raakte zoek, that would not show the sequence as clearly.

Because Dutch does not always use the equivalent of have for perfect tenses.

Some verbs use zijn instead of hebben as their perfect auxiliary, especially verbs that describe:

• movement
• change of state
• something happening to the subject

Zoekraken is treated as a change-of-state verb, so it takes zijn:

• het pakket is zoekgeraakt
• het pakket was zoekgeraakt

Even though English says had gotten lost, Dutch says was zoekgeraakt.

Yes, you may also encounter ... dat het pakket zoekgeraakt was.

Both orders exist in Dutch verb clusters:

• was zoekgeraakt
• zoekgeraakt was

In standard Dutch from the Netherlands, was zoekgeraakt is very common and natural.
The other order can also occur, and some regional or stylistic preferences differ.

So for a learner, the important thing is:

• both can be correct
• was zoekgeraakt is a very safe choice here