Understanding Low Gas Prices Transactions

Can you explain why and how some addresses are permitted to send transactions with a gas price as low as 1 Gwei? In my understanding, fees are setted at a minimum of 3 Gwei.

Here is an example of such a transaction: BNB Smart Chain Transaction Hash (Txhash) Details | BscScan

Any insights or explanations on this would be greatly appreciated. Thank you!

Some validators may accept lower gas fee to include more tx in their blocks.

So, why when I try to send a tx with 1 Gwei fee, it throws me the error that only 3+ Gwei is permitted?
I also tried using multiple RPCs.

Which RPCs are used?

I have tried some of the public ones and one private from QuickNode.