Αν δεν επισυνάψεις το σωστό συνημμένο, η αίτηση δεν προχωράει.

Because after αν in this kind of condition, Greek usually uses the subjunctive, not the ordinary indicative.

Here, επισυνάψεις is the aorist subjunctive of επισυνάπτω. It refers to a single, complete action: attach.

So:

• αν δεν επισυνάψεις = if you do not attach
• αν δεν επισυνάπτεις would sound more like a habitual or ongoing action, which is not what this sentence means

In this sentence, the speaker means one specific action that must be completed correctly.

Because αν itself can introduce the subjunctive in conditional clauses.

Greek often uses:

• αν + subjunctive = if ...

So:

• αν δεν επισυνάψεις = if you do not attach

You do not add να here.
Compare:

• Πρέπει να επισυνάψεις το αρχείο. = You must attach the file.
• Αν επισυνάψεις το αρχείο... = If you attach the file...

So να is not missing; it is simply not used after αν in this structure.

It comes from επισυνάπτω, which means to attach, especially in formal or technical contexts such as documents, emails, or applications.

The form επισυνάψεις is:

• 2nd person singular
• aorist subjunctive
• active voice

So it means you attach / you should attach / you may attach, depending on context.
In this sentence, with αν δεν, it means if you do not attach.

Because Greek usually leaves subject pronouns out when they are not needed.

The ending of επισυνάψεις already tells you the subject is you (singular).

So Greek normally says:

• Αν δεν επισυνάψεις...

rather than:

• Αν εσύ δεν επισυνάψεις...

Adding εσύ would usually give emphasis, something like:

• if you specifically do not attach...

But in a normal instruction or warning, Greek just omits it.

Because συνημμένο is a neuter singular noun here, and the article and adjective must agree with it.

So:

• το = neuter singular article
• σωστό = neuter singular adjective, correct
• συνημμένο = neuter singular noun, attachment

All three match in gender, number, and case.

That is why it is:

• το σωστό συνημμένο

and not:

• ο σωστός συνημμένος
• τον σωστό συνημμένο

Συνημμένο originally comes from a participial form meaning attached, but in modern Greek it is very commonly used as a noun meaning attachment.

So in everyday use, especially in emails, online forms, and office language:

• το συνημμένο = the attachment
• τα συνημμένα = the attachments

This is very common and natural Greek.

It is in the accusative case because it is the direct object of επισυνάψεις.

You are attaching something, namely:

• το σωστό συνημμένο

So the structure is:

• επισυνάψεις = attach
• το σωστό συνημμένο = the correct attachment

The verb acts directly on that noun phrase, so accusative is required.

Because each clause has its own negated verb.

1. Αν δεν επισυνάψεις...
   = If you do not attach...

2. η αίτηση δεν προχωράει
   = the application does not proceed

Greek does not let one negative automatically cover both clauses. Each verb that is negative gets its own δεν.

Literally, προχωράει means goes forward, moves on, or progresses.

In this context, it is used in a very common bureaucratic or technical sense:

• η αίτηση δεν προχωράει = the application does not proceed
• in natural English, this might also be the application cannot move forward or the application will not be processed further

So this is not physical movement; it means the process cannot continue.

Yes, essentially.

Both are forms of προχωρώ:

• προχωράει
• προχωρεί

Both are used in Modern Greek.
Very broadly:

• προχωράει often sounds a bit more everyday and conversational
• προχωρεί can sound slightly more formal or more typical of careful written style

In this sentence, προχωράει is completely normal.

Because the sentence is stating a general rule or system condition, not just one future event.

Greek often uses the present tense in the main clause for this kind of meaning:

• η αίτηση δεν προχωράει = the application does not proceed

This is like saying:

• If X happens, Y does not happen
• If the correct file is missing, the process stops

If the speaker wanted to focus on one specific future instance, Greek could also say something like:

• Αν δεν επισυνάψεις το σωστό συνημμένο, η αίτηση δεν θα προχωρήσει.

That would mean more specifically:

• If you do not attach the correct attachment, the application will not proceed.

But the present-tense version is very common for instructions, rules, and system messages.

Yes.

Greek can also say:

• Η αίτηση δεν προχωράει αν δεν επισυνάψεις το σωστό συνημμένο.

This means the same thing:
The application does not proceed if you do not attach the correct attachment.

When the if-clause comes first, Greek normally uses a comma:

• Αν δεν επισυνάψεις..., η αίτηση δεν προχωράει.

When the main clause comes first, the comma is often omitted.

Because the sentence begins with a conditional clause:

• Αν δεν επισυνάψεις το σωστό συνημμένο

and then moves to the main clause:

• η αίτηση δεν προχωράει

When the conditional clause comes first, Greek normally separates it with a comma, just as English often does:

• If you don’t attach the correct attachment, the application won’t proceed.

So the comma marks the boundary between the two parts of the sentence.