What is a 2.99 transaction fee?

Excuse me, could you please clarify what exactly a 2.99 transaction fee entails? Is this a percentage of the total transaction amount, or is it a fixed amount regardless of the size of the transaction? And furthermore, does this fee apply to all types of cryptocurrency transactions, or are there certain exceptions or conditions that must be met? Understanding the specifics of this fee is crucial in making informed financial decisions, so I would greatly appreciate any clarification you could provide.