Where do I actually pay a visit visa overstay fine in Dubai?

All three answers you have heard are partly true, which is why it sounds contradictory. For a Dubai visit visa, overstay fines sit with the GDRFA, and you can settle them three ways: online through the GDRFA website or app, in person at an Amer centre, or at the airport's immigration counters when you exit. The right choice is about risk, not validity. Paying in advance — online or at an Amer centre — is the safest route: the fine is calculated, paid and receipted before you book your flight, and you pass through departure without surprises. Paying at the airport works and many people do it, but it means arriving several hours early, queueing at the immigration counter, and discovering the final amount only at the moment of travel; if anything unexpected sits on your file, you can miss the flight sorting it out. Given your overstay is only about three weeks and the cause was a family emergency, also ask at the Amer centre whether any reduction is possible for documented circumstances before you pay — it costs nothing to ask. Keep the payment receipt until you have exited. For complicated files, a lawyer or a registered typing centre can settle the fines on your behalf before you travel.