Learn Hardcore Japanese: soukisiharai wo suru to, waribiki ga arimasu.

早期 means “early” or “earlier than usual,” and 支払い means “payment.”
Together, 早期支払い refers to making a payment before the standard due date (“early payment”).

Why is it 支払いをする instead of just 支払う?

支払い is a noun (“payment”). To turn it into the verbal idea “to make a payment,” Japanese uses ～をする: 支払いをする (“to do a payment”).
If you prefer a single verb, you can say 早期に支払う (“to pay early”), but you wouldn’t say 早期支払う without に.

What does the particle と do in すると?

Why is there a comma (、) after する?

The comma marks a brief pause between the conditional clause (早期支払いをすると) and the result clause (割引があります).
It’s not strictly required but improves readability in written Japanese.

Why is it 割引があります instead of 割引です?

あります expresses existence: “there is/are.”
割引があります means “there is a discount” (i.e. “you get a discount”).
割引です would just label something as “a discount,” which doesn’t convey “you receive one.”

Could we replace と with ば or たら here?

Yes. All three form conditionals, but nuance differs slightly:

～と gives a general/inevitable result (“whenever/if you ever…”).
～ば focuses on “if” (“if you do it, then…”).
～たら is more colloquial and often implies “once/after.”
Example: 早期支払いをすれば、割引があります or 早期支払いをしたら、割引があります.

How would I make this sentence more polite or honorific?

In formal business Japanese, you’d use honorific verbs and ございます: “早期にお支払いいただくと、割引がございます。”

Why is there no subject in the sentence?

Japanese often omits subjects when context makes them clear.
Here it’s understood to be “you” or “customers,” so stating あなたが or お客様が is unnecessary.

How do you pronounce 早期 and 割引?

Could we use 割引されます or 割引を受けます instead of 割引があります?

割引されます (passive) means “is discounted” and is grammatically okay:
早期支払いをすると割引されます。
割引を受けます means “receive a discount”:
早期支払いをすると割引を受けます。
However, 割引があります is the simplest and most direct way to say “there is a discount.”