How To Accept Payments For An Advertising Agency

An advertising agency bills on retainers, project milestones, and pass-through media spend, and those three flows behave so differently that treating them as one payment problem is how agencies end up funding their clients' campaigns out of their own bank account. Here is the setup that keeps retainers automatic, milestones enforceable, and media money out of your working capital.

Figures current to July 28, 2026 and rechecked each quarter.

How agency money actually arrives

Four flows. Monthly retainers: the recurring core, invoiced on a fixed date for an agreed scope. Project fees: campaign work, brand builds, launches, billed at milestones rather than on completion. Media pass-through: client ad spend that moves through your accounts to platforms, which is not revenue and must never be treated as such. And performance or commission arrangements where the agency earns a percentage. The machinery is invoicing with stored payment methods, milestone scheduling, and a hard rule about whose money is whose.

By the numbers (July 28, 2026)

This money arrives at 3.3% + 30¢ online or on a card-paid invoice under Square's 2026 pricing. Take a $6,500 monthly retainer and the fee is $215, against $10.00 on ACH, where the 1% rate caps at $10, saving $205. At agency ticket sizes the rail choice is a real line item, which is why bank transfer belongs on every retainer and milestone invoice you send.

The media spend problem, which comes first

An agency placing media on a client's behalf can find itself owing platforms money the client has not yet paid, and that gap has closed more agencies than bad creative ever has. Three defensible structures: the client pays platforms directly on their own card, which removes the risk entirely; the client prepays media into your account before any spend, replenished as it draws down; or you invoice media in advance with terms that stop spend when payment lapses. What is not defensible is fronting media on net-30 terms against a client who pays net-60, because that is an interest-free loan you did not agree to make.

Retainers on autopay, not on invoices you chase

The retainer is the agency's stability, and it should behave like a subscription rather than a monthly negotiation. The agreement states the scope, the monthly fee, the billing date, and the authorization to charge a stored method automatically. Charges land on a fixed date with the invoice sent ahead, not after. Scope changes get a written amendment before they bill. And late payment terms exist and are applied, because an agency that never enforces them trains clients that the date is optional, which is exactly how a healthy retainer becomes a receivable.

Milestones on project work

Campaign and build work bills in stages tied to deliverables, not to calendar months: a deposit at signing before any work begins, a payment at strategy or concept approval, and the balance at delivery. Each milestone is defined in the statement of work with what triggers it, so nobody negotiates at the moment of invoicing. Revision rounds are counted, and additional rounds are quoted in writing. The deposit is the part agencies skip most often and regret most reliably, since work started without money is work a client can walk away from at no cost.

Rails, tickets, and what each flow should use

Match the rail to the amount. Retainers and small project fees run comfortably on card, where convenience is worth the percentage. Large milestone payments and any media prepayment belong on bank transfer, because at four and five figures the fee difference is real money rather than a rounding error. Offer both on every invoice and let the client choose, and put the bank details where they are easy to find, since the clients most likely to use them are the ones sending the largest amounts.

Sources

• Swipesum — Square Fees Explained 2026 (verified against Square's published pricing)
• NerdWallet — Square Fees: Calculator and Pricing for 2026

What people ask me

How should an advertising agency handle client media spend?

Three safe structures: the client pays platforms directly, prepays media into your account before spend, or is invoiced in advance with spend stopping if payment lapses. Never front media on mismatched terms.

How should agency retainers be billed?

Like a subscription: a stored payment method charged automatically on a fixed date, with the invoice sent ahead, scope changes amended in writing, and late terms actually enforced.

How should project work be invoiced?

At milestones tied to deliverables: a deposit at signing before work begins, a payment at concept or strategy approval, and the balance at delivery, each defined in the statement of work.

Why does the deposit matter so much?

Work started without money is work a client can walk away from at no cost, which is the single most common way agencies lose a project's value entirely.

Which payment rail suits which flow?

Card for retainers and small fees where convenience is worth the percentage; bank transfer for large milestones and media prepayments, where the fee difference is real money.

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