Thank you, everyone! Finally, the Support team removed the warning after reviewing my account, and I want to express my gratitude to them. The actual reason for the warning is unbelievable.
The reason is last month, I did a project for a German student. After he informed me of an issue with his payment method, he asked if his uncle could pay instead. I advised him to have his uncle contact me via Fiverr, and then I sent an offer to him. Finally, I delivered the order to his uncle. This is the reason for the warning. My only purpose was to satisfy my client, but ultimately, I received a warning. So, guys, be careful about this.