Why do I have an unpaid transaction fee?

Excuse me, could you please clarify for me why I am facing an unpaid transaction fee? I've been making transactions in cryptocurrency for some time now, and I've never encountered this issue before. Is there a specific reason why this fee hasn't been settled, or is it something that's been recently introduced? I'd really appreciate it if you could provide me with some insight into this matter. Thank you in advance for your assistance.