Use this when the job is $10,000 and the customer pays half up front.
The invoice stays at $10,000. The customer sees the full value of the work, and below it a highlighted line showing what to pay now. The card button charges that figure, not the total.
Percentage or amount
A percentage survives an edit: correct the invoice to $12,000 and half becomes $6,000 on its own. A fixed amount does not move — use it when both sides agreed on a figure rather than a fraction.
What it does not change
Nothing in your books. The sale is still $10,000 and still posts to Accounts Receivable in full. This only changes one line on the document and what the pay button asks for.