Instant payment apps like Venmo and Apple Cash make it easy to send money to friends or family. But they’ve also given scammers another way to defraud unsuspecting users.

Here’s how the latest scam often starts: You get a payment from a number you don’t recognize. A few hours or days later, the sender messages you, "Oh, I accidentally sent those funds to the wrong number! I was trying to send my brother-in-law that $3,000! Can you send it back?"

It might sound like an honest mistake. Often, it’s not. This is known as an accidental deposit scam, and it can cost you thousands.

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How do payment app scams work?

In an accidental deposit scam, fraudsters use stolen credit cards or bank account information to send money to random users on apps like Zelle, Apple Cash, Venmo or PayPal. They’ll quickly follow up with a message claiming it was a mistake and pressure you to return the funds.

Their goal is to get you to transfer your own money to them, which they withdraw immediately. Once the real account owner notices the fraud, their bank reverses the payment, withdrawing it from your account. By then, the scammer is long gone with the money you sent back, leaving you on the hook.

Signs you may be dealing with a scammer include:

Even if the money shows up in your account, you don’t have the right to spend it. Like stolen property, it doesn’t belong to you. The safest move is to leave the money alone, notify the app and wait. If the funds were truly sent in error, the app can refund them. If it’s fraud, your caution will protect you from being scammed.

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What should you do if someone you don’t know sends you money?

If a stranger sends you money through a payment app, do not send it back under any circumstances. Not if they claim to be in crisis, not if they threaten violence and not if they say the app won’t let them reverse the charge.

Instead:

Payment app companies can investigate and remove funds sent in error. If it’s not a scam — though it likely is — the sender will have to go through official channels to resolve it.

Scammers may escalate if you don’t respond, calling or texting repeatedly, accusing you of theft or threatening legal action. These are scare tactics. Don’t engage. Let the payment app handle it.

The bottom line: An unexpected deposit followed by a desperate plea to return the funds is almost always a scam. Let the app or your bank deal with it, and never let anyone guilt you into sending money. If you send the funds yourself, it’s not considered fraud, and you won’t get a refund.

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This article originally appeared on Moneywise.com under the title: I was sent $3K from a random number. The stranger said it was a mistake — then accused me of stealing. Is this a scam

This article provides information only and should not be construed as advice. It is provided without warranty of any kind.