Subsanamos la solicitud, pues falta un justificante de gasto.

In this context, subsanar is a formal, administrative verb. It means something like:

• to correct
• to remedy
• to fix a deficiency
• to complete something that was incomplete

So subsanamos la solicitud is not everyday Spanish like arreglamos or corregimos. It sounds official and bureaucratic, especially in forms, public administration, and legal contexts.

With la solicitud, it usually means we amend / rectify the application because something is missing or needs to be fixed.

Because Spanish often leaves out subject pronouns when the verb ending already shows who the subject is.

• subsanamos = we correct / amend
• the ending -amos already tells you it is nosotros

So:

• Subsanamos la solicitud
• Nosotros subsanamos la solicitud

both mean the same thing, but the version without nosotros is more natural unless you want emphasis or contrast.

Good question: subsanamos can be either:

• present indicative: we correct / we are correcting / we hereby correct
• preterite: we corrected

The form is identical.

In this sentence, it is most likely understood as present, especially because the rest of the sentence is also in the present:

• pues falta un justificante de gasto = since a proof of expense is missing

So the whole sentence sounds like an administrative statement about the current situation.

La solicitud refers to a specific application that both speaker and listener already know about.

In administrative Spanish, this is very common. The document is already identified by the context, so the definite article is used:

• la solicitud = the application
• una solicitud = an application / one application

If someone writes this in a notice or message, they usually mean your application or the application in question, not just any application.

Here pues means since, because, or as.

So:

• Subsanamos la solicitud, pues falta un justificante de gasto. = We amend the application, since a proof of expense is missing.

It is similar to porque, but pues often sounds a bit more formal or written, especially in this type of bureaucratic language.

Compare:

• porque falta un justificante de gasto = straightforward because
• pues falta un justificante de gasto = slightly more formal/literary/administrative since / as

In modern everyday speech, porque is usually more common.

Faltar literally means to be missing or to be lacking.

The important thing is that the thing missing is the grammatical subject.

So here:

• un justificante de gasto = the subject
• falta = is missing

Literally, it is closer to:

• A proof of expense is missing

not:

• Someone misses a proof of expense

That is why faltar is often different from English in structure.

For example:

• Falta un documento. = A document is missing.
• Faltan dos documentos. = Two documents are missing.

Because the subject is singular:

• un justificante de gasto = one supporting document / one receipt / one proof of expense

So the verb must also be singular:

• falta un justificante
• faltan dos justificantes

If the sentence were plural, it would change to:

• faltan varios justificantes de gasto

It is a very common administrative expression in Spain. It means a document that proves an expense.

Depending on the context, it could be:

• a receipt
• an invoice
• a proof of payment
• supporting documentation for an expense

So justificante is broader than just receipt. It is any document used to justify or prove that money was spent.

That is why in official contexts justificante de gasto is often better understood as:

• proof of expense
• supporting expense document

rather than only receipt

Because justificante de gasto is being used as a general category: expense proof / proof of expense.

• de gasto = about expenses / for expense justification in general
• del gasto = of the specific expense

So:

• un justificante de gasto = an expense-supporting document
• el justificante del gasto = the document for that specific expense

Both are possible, but they mean slightly different things.

Yes, it is natural in Spain, but it is clearly formal administrative Spanish.

A native speaker would recognize this as the kind of wording used in:

• public administration
• university paperwork
• grant applications
• legal or official notifications

It does not sound like casual conversation.

A more everyday version might use simpler wording, for example:

• Corregimos la solicitud porque falta un justificante de gasto.
• Hay que completar la solicitud porque falta un justificante de gasto.

But the original sentence sounds exactly like official paperwork, which is probably the point.

In administrative Spanish, subsanar la solicitud usually means to remedy a defect in the application. Very often that means:

• adding a missing document
• correcting an error
• completing missing information

So it does not necessarily mean rewriting the whole application. It usually means bringing it into proper form so it can be processed.

That is why the second part explains the problem:

• pues falta un justificante de gasto

In other words, the application needs to be put right because one required supporting document is missing.