If you’re a digital marketer who truly needs established accounts (e.g., for ad accounts with history), there are grey-market vendors who sell accounts created legitimately, then transferred. Caveats:

Link a valid mobile phone number to pass the initial two-factor authentication (2FA) check.

: Using shared accounts or creating accounts with false information violates Meta's Terms of Service

Let me know which direction you’d like to take, and I’ll write a complete, safe, and useful post for you.

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: Facebook’s security systems immediately flag and permanently ban accounts accessed from unfamiliar IP addresses, device signatures, or locations, making leaked public credentials useless. Safe and Legitimate Alternatives

The harm is that you’re still breaking the law and violating Facebook’s Terms. For legitimate testing, Facebook provides and test users via the Facebook for Developers platform. You can create as many fake, sandboxed accounts as you need – legally and for free.

Here are some and information that might be relevant, focusing on legitimate and safe practices:

Regularly check your account's login history and activity for any suspicious actions.