Your ROAS Got Devalued and You Never Touched a Campaign

On October 6 the dollar closed below 17 Mexican pesos. On October 21 it closed at 18.67, capping seven straight weeks of peso losses. In those three weeks nobody on your team paused a campaign, changed a bid, or edited an audience. Media still got about 10% more expensive.

Here is the uncomfortable part: across Latin America media cost is effectively dollarized and revenue almost never is. That target ROAS —the 3.2 somebody typed into a spreadsheet in January— is not a marketing number. It is an unhedged currency bet.

You buy in one currency and get paid in another

The Meta or Google auction charges in the ad account currency. The actual money leaves a card, and two things happen there: the platform converts at its own rate, not the central bank rate, and the issuing bank adds a cross-border fee that in the region usually runs 1% to 3%. If the account is in dollars and your cash sits in quetzales, bolívares or pesos, every charge is an FX trade wearing an advertising invoice.

Revenue, meanwhile, arrives in local currency. So ROAS —local revenue over dollarized cost— moves on its own. An 8% devaluation at identical volume and identical CPM is 8% less margin, with nothing done wrong by the person buying media. It cuts the other way too: when the currency strengthens, the dashboard congratulates you for an optimization you never made.

The region is not one case

• Panama is dollarized. No FX risk — only the risk of assuming everyone else works the same way.
• Guatemala has kept the quetzal inside a narrow band for years. The risk there is not devaluation, it is complacency: processes get designed in that calm and then exported to Mexico or Chile, where they break.
• Chile sits around 985 pesos to the dollar, volatile enough to make a locked quarterly budget a work of fiction.
• Mexico is the case opening this piece, and it came from seven weeks of decline rather than one bad session.
• Venezuela is the extreme: an official rate and a parallel rate coexisting, payments routed through third parties or foreign cards, and a margin that can disappear between the day a budget is approved and the day the charge actually clears.

A regional plan running one target ROAS across all five markets is not simplification. It is a measurement error dressed up as efficiency.

Three places the money leaks

1. Account currency. In both Meta and Google Ads the currency is set when the account is created and cannot be changed afterward. Switching means a new account and everything that drags along: learning history, conversion setup, billing, permissions. Most teams discover this at the point where fixing it is expensive. Which currency an account lives in is a finance decision, not a dropdown on a signup form.

2. Payment method. Local card, dollar card, authorized reseller, or an agency that invoices in local currency at its own rate — each path carries a different cost, and almost nobody lines them up in a table. A 4% markup on an agency credit line outweighs much of what teams agonize over inside the auction.

3. The frozen target. Break-even gets calculated once a year and quoted for twelve months. If FX moved 10%, your maximum CPA moved too. Buying against the old number means buying leads that no longer carry margin and reporting them as a good month.

What to do on Monday

• Track two numbers, not one: CPA in local currency, which is what finance sees, and CPA in dollars, which is what the auction sees. When they diverge, you already know the problem is not the creative.
• Recompute break-even ROAS monthly at the closing rate, not at the annual budget rate. It is ten minutes of spreadsheet work.
• Set a band: past a defined percentage move, a pricing or target review triggers automatically. Without a band, the decision gets made late and out of panic.
• Do not cut budget because of an FX headline. Cut on margin. These are different things and they get confused constantly.
• If you sell imported goods, the hit lands twice: media and cost of goods rise together. That calls for a price change, not a bid change.

The two lines nobody overlays

We spend months arguing attribution — whether Meta over-credits itself, whether GA4 swallows direct traffic, whether last click lies — while a variable that shifted real cost 10% in three weeks appears in no report at all. Attribution matters; the problem is that it is being used to explain a gap with a different cause.

Try something simple: plot monthly ROAS and lay the exchange rate on top of it. If the two move together, the conversation with the client or the CFO changes register. You stop defending a campaign and start explaining an exposure — and that is a conversation where marketing actually has proposals: pricing, market mix, invoicing currency, when the account gets topped up, how much prepaid balance is worth holding.

Paid media in Latin America is not managed only in the ads manager. It is also managed in the sheet where the exchange rate lives. Watch just one of the two and eventually you get wiped out without understanding why.