TDS on Commission 194 H

"Provided that no deduction shall be made under this section in a case where the amount of such income or, as the case may be, the aggregate of the amounts of such income credited or paid or likely to be credited or paid during the financial year to the account of, or to, the payee, does not exceed fifteen thousand rupees."

So, when the total payment crosses 15k, deduct TDS, if applicable.

It can be a against a single invoice or multiple invoice, that doesn't matter. Just check the total payments made in a FY for applicability.