Kvůli premiéře jsme koupili vstupenky v předprodeji.

Because kvůli requires the dative case.

The basic form is premiéra (premiere, opening night), but after kvůli it becomes premiéře.

• premiéra = nominative
• kvůli premiéře = dative

So this is a standard pattern:

• kvůli koncertu
• kvůli škole
• kvůli premiéře

A good rule to remember is: kvůli + dative.

Not exactly.

• kvůli usually means because of, due to, or for the sake of
• protože means because and introduces a full clause

So:

• Kvůli premiéře jsme koupili vstupenky v předprodeji.
  = Because of the premiere / Due to the premiere, we bought the tickets in presale.

But with protože, you would normally need a full sentence after it:

• Koupili jsme vstupenky v předprodeji, protože byla premiéra.
  = We bought the tickets in presale because it was a premiere.

So kvůli is followed by a noun phrase, while protože is followed by a clause.

This is the normal Czech past tense.

Czech past tense is usually made from:

1. a past participle
2. a present form of být (to be)

Here:

• jsme = we are / auxiliary for we in the past tense
• koupili = past participle of koupit (to buy), masculine animate/inanimate plural form used for a mixed or masculine group, or often as the default for we

Together:

• jsme koupili = we bought

Other examples:

• jsem koupil/koupila = I bought
• jsi koupil/koupila = you bought
• jsme koupili = we bought
• jste koupili = you bought
• koupili = they bought

Both are possible.

Czech word order is more flexible than English, and both of these can be natural:

• Kvůli premiéře jsme koupili vstupenky v předprodeji.
• Kvůli premiéře koupili jsme vstupenky v předprodeji. → possible, but less natural
• Kvůli premiéře vstupenky jsme koupili v předprodeji. → possible only in special emphasis

The most natural options are usually:

• Jsme koupili...
• Koupili jsme...

In this sentence, jsme koupili sounds neutral after the opening phrase Kvůli premiéře.

Also, jsme is a clitic-like auxiliary, so it often appears in the second position of the sentence or clause:

• Kvůli premiéře jsme...

That is one reason this word order feels natural.

Here vstupenky is in the accusative plural, because it is the direct object of koupili (bought).

Basic forms:

• singular: vstupenka = ticket
• plural nominative: vstupenky
• plural accusative: vstupenky

For this noun, the nominative plural and accusative plural look the same.

So:

• Vstupenky jsou drahé. = The tickets are expensive.
  (vstupenky = nominative plural)

• Koupili jsme vstupenky. = We bought tickets.
  (vstupenky = accusative plural)

V předprodeji means something like in presale, in advance sale, or more naturally in English, in advance / during presale.

The noun is:

• předprodej = presale, advance sale

And the phrase:

• v předprodeji = in presale / on presale / in advance sale

In context, it means the tickets were bought before the event in the official advance sales period, not at the door.

Common examples:

• Vstupenky jsou v předprodeji. = Tickets are on presale.
• Koupili jsme je v předprodeji. = We bought them in advance / during presale.

Because the preposition v here requires the locative case when it means in or inside a situation/place.

The base noun is:

• předprodej

But after v, it changes to:

• v předprodeji

This is a common pattern:

• v obchodě = in the shop
• v kině = in the cinema
• v předprodeji = in presale

So the ending -i shows the locative singular here.

Yes. Premiéra is fairly broad.

It can mean:

• a film premiere
• a theatre premiere
• an opera or concert premiere
• more generally, the first public performance/showing

The exact meaning depends on context. The sentence itself does not specify what kind of premiere it is.

So a Czech speaker would understand premiéra as the first showing/performance, and the surrounding situation would tell you whether it is a movie, play, etc.

Yes, koupili is the plural past form used for a group that is:

• masculine animate, or
• mixed, or
• often a general/default plural in many contexts

If the group were only women, standard Czech would use:

• Kvůli premiéře jsme koupily vstupenky v předprodeji.

So:

• jsme koupili = we bought (men / mixed group / general)
• jsme koupily = we bought (women only)

This gender distinction appears in the past tense in Czech, which is something English does not do.

In very informal spoken Czech, people sometimes reduce or omit auxiliaries in certain contexts, but for learners you should treat jsme as necessary here.

Standard Czech is:

• Kvůli premiéře jsme koupili vstupenky v předprodeji.

If you leave out jsme, it may sound colloquial, dialectal, or simply non-standard depending on the context.

So the safest rule is:

• in normal written and spoken Czech, keep jsme

Yes, and that is very natural.

Adding si gives the sense that we bought the tickets for ourselves.

Compare:

• Jsme koupili vstupenky. = We bought tickets.
• Jsme si koupili vstupenky. = We bought ourselves tickets. / We bought tickets for ourselves.

In many everyday situations, Czech speakers often use si with actions like buying when the thing is for their own use.

So both are correct, but:

• without si = neutral
• with si = slightly more personal/reflexive, often very natural in conversation

Yes, it is natural and correct.

It sounds like a normal sentence meaning that, because it was a premiere, the speakers bought tickets during the presale period.

A native speaker might also say similar variants, for example:

• Kvůli premiéře jsme koupili lístky v předprodeji.
• Na premiéru jsme koupili vstupenky v předprodeji.
• Vstupenky jsme kvůli premiéře koupili v předprodeji.

But your original sentence is completely fine and idiomatic.