a customer got refunded on Shopify, how does that show in my books

A refund flows through the same payout that carried the sale, and Talisk reverses both sides of it.

Concretely, when you refund an order:

• the revenue is reversed, so your sales figure drops by the refunded amount
• the sales tax you'd collected is reversed too: you're no longer holding it
• if cost tracking is on, the COGS is reversed at the original cost, so the returned item doesn't leave a phantom cost sitting in your books
• the refund reduces that period's payout, which is why the deposit is smaller

You don't post anything by hand. The important part is that a refund is a reversal, not a new expense: recording it as a cost would understate revenue and overstate expenses at the same time, and quietly distort your margin.