رقم الطلب في الرسالة.

In present-tense Arabic, a sentence like this often has no expressed verb for is/are.

So رقم الطلب في الرسالة is literally something like:

• order number
• in the message

Arabic naturally understands this as The order number is in the message.

If you wanted past tense, you would usually add a verb such as كان:

• كان رقم الطلب في الرسالة = The order number was in the message

Because رقم الطلب is an iḍāfa construction, often called a genitive construction or noun-noun possessive construction.

In an iḍāfa:

• the first noun usually does not take الـ
• the second noun can be definite or indefinite
• the whole phrase gets its definiteness from the second noun

So:

• رقم الطلب = the order number / the number of the order

But:

• الرقم الطلب is not standard Arabic here

This is one of the most important structures in Arabic.

It is an iḍāfa:

• رقم = number
• الطلب = the order / the request

Together, they mean:

• the number of the order
• or more naturally in English, the order number

In this structure:

1. the first noun (رقم) is the thing being described or possessed
2. the second noun (الطلب) specifies it
3. English may translate it with of or with a compound noun

So Arabic uses noun + noun, where English might use either:

• the number of the order
• the order number

Because in an iḍāfa, the second noun can carry definiteness for the whole phrase.

Here:

• الطلب = the order
• therefore رقم الطلب becomes the order number, a definite phrase

So even though رقم itself has no الـ, the whole expression is definite because the second noun is definite.

Compare:

• رقم طلب = an order number / a request number
• رقم الطلب = the order number

في means in.

After a preposition like في, the following noun is in the genitive case.

So:

• في الرسالة = in the message

If fully vowelled, it would be:

• في الرِّسالةِ

The final ـِ is the genitive case ending.

In normal everyday Arabic writing, these short vowel endings are usually not written, so you just see:

• في الرسالة

A fully vowelled version would typically be:

رَقْمُ الطَّلَبِ فِي الرِّسَالَةِ.

This shows:

• رَقْمُ: nominative, because it is the subject/topic of the nominal sentence
• الطَّلَبِ: genitive, because it is the second term of the iḍāfa
• الرِّسَالَةِ: genitive, because it comes after في

In normal unvowelled writing, all of those endings are usually omitted.

A careful full reading is approximately:

raqmu ṭ-ṭalabi fī r-risālati

A pause-form reading, which is very common in real life, is closer to:

raqm aṭ-ṭalab fī ar-risāla

Two pronunciation points matter here:

• الطلب is pronounced aṭ-ṭalab, not al-ṭalab, because ط is a sun letter, so the l sound assimilates
• الرسالة is pronounced ar-risāla, not al-risāla, because ر is also a sun letter

The final ة is called tāʾ marbūṭa.

Its pronunciation depends on context:

• when pausing at the end, it is usually pronounced like -a (sometimes with a very slight h quality)
• when followed by a grammatical ending or when connected in certain contexts, it is pronounced like t

So:

• in pause: ar-risāla
• with case ending in careful reading: ar-risālati

That is why learners may hear both kinds of pronunciation.

No. طلب has a broader meaning range than the English word order.

Depending on context, it can mean:

• request
• application
• demand
• order

So رقم الطلب can mean different things in different situations, such as:

• order number in shopping/customer service
• request number
• application number

Context tells you which English meaning is best.

It can be understood as a complete nominal sentence:

• رقم الطلب في الرسالة = The order number is in the message

But depending on context, it could also function as a short fragment, especially in:

• app interfaces
• instructions
• headings
• customer-service messages

For example, it might mean something like:

• Order number: in the message
• or a shortened reminder equivalent to The order number is in the message

Arabic often allows this kind of compact wording.

Yes. That would also be natural.

• رقم الطلب في الرسالة = shorter, more compact
• رقم الطلب موجود في الرسالة = more explicit, with موجود meaning present / found / there

Both can work, but the version without موجود is very common and perfectly normal in Arabic, especially in concise written language.