Ich zeige an der Kasse meine Kundenkarte, damit ich den Rabatt bekomme.

I show my customer card at the checkout so that I get the discount.

Breakdown of Ich zeige an der Kasse meine Kundenkarte, damit ich den Rabatt bekomme.

• ich: I
• zeigen: to show
• mein: my
• damit: so that
• den: the; (masculine, accusative)
• an: at
• der: the; (feminine, dative)
• die Kasse: the checkout
• der Rabatt: the discount
• bekommen: to get
• die Kundenkarte: the customer card

Questions & Answers about Ich zeige an der Kasse meine Kundenkarte, damit ich den Rabatt bekomme.

Why is it an der Kasse and not in der Kasse or bei der Kasse?

an der Kasse means “at the checkout/cash register” in the sense of “at that station/spot.”

• in der Kasse would literally mean “in the cash register / in the cash box,” i.e., inside it.
• bei der Kasse can also mean “at/near the checkout,” but it often feels more like “near/next to” rather than “right at the point of paying.” an der Kasse is the most idiomatic for “at the checkout.”

Why is it der Kasse (dative) and not die Kasse (accusative)?

Because an is a “two-way preposition.”

• With a location (no movement), it takes dative: an der Kasse = “at the checkout.”
• With a destination/movement toward, it takes accusative: an die Kasse gehen = “go to the checkout.”

Why is meine Kundenkarte in that form—what case is it?

It’s accusative, because zeigen takes a direct object (what you show).

• ich = subject (nominative)
• meine Kundenkarte = direct object (accusative)

Why does damit cause the verb to go to the end in …, damit ich den Rabatt bekomme?

damit introduces a subordinate clause (a dependent clause of purpose). In German subordinate clauses, the conjugated verb goes to the end:

• …, damit ich den Rabatt bekomme. (verb bekomme at the end)

Is the comma before damit mandatory?

Yes. A subordinate clause introduced by damit is normally separated by a comma:

• Ich zeige …, damit ich … bekomme.
  In standard written German, leaving out that comma is considered incorrect.

What’s the difference between damit ich den Rabatt bekomme and um den Rabatt zu bekommen?

Both express purpose (“so that / in order to”), but they’re structured differently:

• damit + finite verb: …, damit ich den Rabatt bekomme.
• um … zu + infinitive: …, um den Rabatt zu bekommen.

A common rule of thumb:

• Use um … zu when the subject is the same in both clauses (here it is: ich → ich), so um den Rabatt zu bekommen would be a very natural alternative.
• Use damit especially when the subject would be different, or when you prefer a full clause.

Why is ich repeated? Can you drop the second ich?

No. In damit-clauses you need an explicit subject if it’s not something like an infinitive construction. German doesn’t allow you to omit the subject the way English sometimes can in informal style. So you need …, damit ich … bekomme.

Why is it den Rabatt—what gender is Rabatt, and is the article necessary?

Rabatt is masculine: der Rabatt. That’s why the accusative form is den Rabatt.
The article is very common because you usually mean a specific discount you’re entitled to in that situation. In some contexts you might hear it without an article (more like “discount” as a general concept), but den Rabatt bekommen is a standard phrasing.

Could I say Ich zeige ... vor or use vorzeigen instead of zeigen?

Yes. In a checkout context, vorzeigen (or zeigen + vor) is very common and can sound more specific, like “present/show (for inspection)”:

• Ich zeige an der Kasse meine Kundenkarte vor, …
• Ich zeige an der Kasse meine Kundenkarte, … (also fine, a bit more general)

Why is Kundenkarte one word and capitalized?

German forms compounds freely: Kunde + Karte → Kundenkarte (a “customer card”).
All nouns are capitalized in German, so Kundenkarte and Kasse and Rabatt are capitalized.

Is the present tense (zeige, bekomme) being used for the future or for a habitual action?

Most naturally, it’s describing a typical/regular action (“I show my customer card at the checkout so that I get the discount”). German present tense commonly covers habitual actions like this.
It can also work for a near-future plan in the right context, but the sentence reads most like a general routine.

Can the sentence start with the damit clause?

Yes. You can front the purpose clause for emphasis. Then the main clause must follow German verb-second rules (the verb comes right after the first element):

• Damit ich den Rabatt bekomme, zeige ich an der Kasse meine Kundenkarte.