haraimodosi ka nitteihenkou wo onegaisuru.

Here, か means or, not the question particle.

So:

• 払い戻し = refund
• か = or
• 日程変更 = change of schedule/date
• をお願いする = request

In other words, A か B means A or B.

The same particle か can also mark a question at the end of a sentence, but here it is connecting two choices, so it means or.

Because 払い戻しか日程変更 works as one combined object: refund or schedule change.

The を applies to the whole choice phrase, not just the second noun.

So the structure is:

• [払い戻しか日程変更] を お願いする

This is very common in Japanese. When two nouns are linked by か, you usually do not need to repeat the particle after each one.

You could think of it like English:

• I request [a refund or a schedule change].

There is only one object for the verb request, even though it contains two options.

お願いする means to request, to ask for, or sometimes to ask someone to do something.

In this sentence, it means:

• to request a refund or a schedule change

A very common everyday form is:

• お願いします

For example:

• 払い戻しか日程変更をお願いします。

That sounds like something you might actually say to staff.

So:

• お願いする = dictionary/plain form
• お願いします = polite form

It sounds more like a plain written form, such as:

• a note
• a memo
• a heading on a form
• a neutral description of an action

In normal conversation, especially with staff, you would more naturally say:

• 払い戻しか日程変更をお願いします。
• 払い戻しか日程変更をお願いしたいです。

Those are more natural spoken options.

So yes, the original sentence is grammatical, but in conversation you would usually use a more polite ending.

Because Japanese often leaves out the subject when it is understood from context.

English usually needs something like:

• I would like to request...
• Can you do...
• We request...

Japanese often does not say that explicitly if the situation makes it obvious.

So in a real setting, 払い戻しか日程変更をお願いします would naturally mean something like:

• I’d like to request a refund or a change of date.

The subject is omitted because it is understood.

In this sentence, both are functioning as nouns.

• 払い戻し = refund
• 日程変更 = schedule change / rescheduling

They are the things being requested.

Japanese often uses noun-like words together with する or with another verb such as お願いする.

Here, they are not the main verbs of the sentence. The main verb is:

• お願いする

So the structure is basically:

• [refund or schedule change] + object marker + request

日程変更する is possible and natural, because 変更する is a very common suru-verb pattern meaning to change.

For example:

• 日程を変更する = to change the schedule/date
• 日程変更する = to reschedule

払い戻し is a little different. In many contexts, Japanese prefers expressions like:

• 払い戻しをする
• 払い戻しをお願いする
• 払い戻しを受ける

rather than a simple 払い戻しする used freely in all situations.

So in this sentence, 払い戻しをお願いする sounds very natural.

Both relate to getting money back, but the nuance can differ.

• 払い戻し often means a refund/reimbursement, especially for things like tickets, reservations, fees, and transportation.
• 返金 is also refund, but often focuses more directly on returning money.

For tickets, bookings, and event/travel situations, 払い戻し is very common and natural.

So if this sentence is about changing or canceling a reservation, 払い戻し fits very well.

日程 usually refers to a schedule, planned date, or itinerary.
日時 means date and time more literally.

So:

• 日程変更 = change of schedule / rescheduling
• 日時変更 = change of date and time

Which one is best depends on context.

If the issue is broadly rescheduling an event, appointment, or booking, 日程変更 is very natural. If the exact time matters and the speaker wants to emphasize both date and time, 日時変更 might be used instead.

Usually A か B is understood as A or B, often with an either/or feel.

In this sentence, it normally suggests:

• a refund
• or
• a schedule change

That is, one of the two options.

However, Japanese か does not always force a strict logical distinction in the way formal logic does. Real meaning comes from context. In most service situations, this phrase would naturally be understood as choosing one of the available options.

No, the nuance changes.

• か = or
• や = things like A and B / a non-exhaustive list

So:

• 払い戻しか日程変更をお願いする = request a refund or a schedule change
• 払い戻しや日程変更をお願いする = request things like a refund and/or a schedule change

For clear alternatives, か is the right choice.

A very natural polite version is:

• 払い戻しか日程変更をお願いします。

If you want to sound softer:

• 払い戻しか日程変更をお願いしたいです。
• 払い戻しか日程変更は可能でしょうか。

These sound more natural when speaking to customer service or staff.

The original お願いする is fine as a dictionary/plain form, but not the most natural final form for polite conversation.

It is pronounced:

• はらいもどし か にっていへんこう を おねがいする

Breakdown:

• 払い戻し → はらいもどし
• か → か
• 日程変更 → にっていへんこう
• を → pronounced お
• お願いする → おねがいする

A learner often notices that を is written を but usually pronounced お in modern Japanese.

A good way to parse it is:

• 払い戻し = refund
• か = or
• 日程変更 = schedule change
• を = object marker
• お願いする = request

So the overall chunking is:

• [払い戻しか日程変更] を [お願いする]

This helps you see that refund or schedule change is one object phrase, and request is the action.

If you mentally group it this way, the sentence becomes much easier to understand.