La entidad emisora prepara la tarjeta de sustitución.

Because emisora agrees with entidad, which is a feminine noun.

• entidad = feminine singular
• so the adjective/noun describing it must also be feminine singular: emisora

This is standard gender agreement in Spanish.
Compare:

• el banco emisor
• la entidad emisora

Even if the thing is not biologically female, grammatical gender still controls the form.

In Spanish, adjectives often come after the noun, especially when they classify or specify what type of thing something is.

So:

• entidad emisora = issuing entity
• literally, something like entity issuing or issuer entity

This post-noun position is very normal in formal or technical Spanish. In English, we usually put the modifier before the noun, but Spanish often does the opposite.

It is a formal expression meaning the organization that issues something, especially a card, document, or financial product.

Depending on context, it could be:

• a bank
• a card company
• another financial institution

So it is broader and more official-sounding than just banco. In administrative or banking Spanish, this kind of wording is very common.

Prepara is the 3rd person singular present indicative of preparar.

Here it matches the subject la entidad emisora.

So grammatically it means:

• the issuing entity prepares
• or, depending on context, is preparing

In Spanish, the present tense can cover several ideas that English often separates:

• a general present: prepares
• something happening now: is preparing
• sometimes even a near-future or procedural meaning in formal contexts

Because Spanish usually does not need subject pronouns when the verb form already shows the person and number, or when the subject noun is stated explicitly.

Here, the subject is already present:

• La entidad emisora prepara...

So adding a pronoun would be unnecessary.

Spanish is a pro-drop language, which means subject pronouns are often omitted unless they are needed for emphasis or contrast.

Because each noun phrase needs its own article here:

• la entidad emisora = the subject
• la tarjeta de sustitución = the direct object

English sometimes avoids repeating the, but Spanish normally uses the article with each definite noun phrase when appropriate.

So the repetition is completely natural.

Spanish often expresses this kind of idea with noun + de + noun.

So:

• tarjeta de sustitución = literally card of replacement
• natural English equivalent: replacement card

This structure is very common in Spanish, especially in formal or technical language. Other examples:

• tarjeta de crédito
• centro de salud
• documento de identidad

English often uses a noun as a modifier, but Spanish usually prefers de or an adjective.

Both sustitución and reemplazo can relate to the idea of replacement, but they are not always equally natural in every context.

In formal Spain Spanish, especially in administrative or banking language, de sustitución sounds very standard and official.

• tarjeta de sustitución = very formal, institutional
• tarjeta de reemplazo = understandable, but may sound less typical in some Spain contexts

So a learner should recognize both, but sustitución fits well in this kind of formal sentence.

The given order is the most neutral and standard one:

• La entidad emisora = subject
• prepara = verb
• la tarjeta de sustitución = object

Spanish word order is more flexible than English, so other orders are possible for emphasis, but they would sound less neutral. For example:

• La tarjeta de sustitución la prepara la entidad emisora

This puts more focus on the replacement card.

For ordinary, straightforward information, the original order is the best choice.

In Spain Spanish, the c before i is usually pronounced like the th in think.

So sustitución is roughly:

• soos-tee-too-THYON in much of Spain

A few useful pronunciation points:

• susti- has a clear s
• -tu-
• -ción has stress on the last syllable because of the written accent: -ción
• the c in ción is the Spain th sound

Also, z in much of Spain has that same th sound, so learners often notice both c and z sounding different from Latin American Spanish.

The accent mark shows where the stress falls:

• sus-ti-tu-ción

Without the accent, Spanish stress rules would make you expect a different stress pattern. The written accent tells you clearly that the final syllable is stressed.

This is also a very common ending in Spanish:

• información
• emisión
• renovación
• sustitución

So it is useful to learn -ción words as a pattern.

In this sentence, it works adjectivally: it describes what kind of entidad it is.

• entidad emisora = issuing entity

But forms like emisor / emisora can also function as nouns in other contexts:

• el emisor = the issuer / sender
• la emisora = the issuer, and in other contexts even radio station

So here, the role is descriptive, but the word itself can behave either as an adjective or as a noun depending on context.