The fixed fee is an amount of ADA taken from the pool’s total rewards in an epoch. This is not a fee charged to each delegator.
For example, suppose the GOAT pool earned 10000 ADA in the past epoch. The protocol automatically deducts 340 ADA as a fixed fee from the 10000 ADA and sends it to our wallet. Therefore 10000-340=9660 ADA is left.
Then variable fee will be calculated and deducted based on the percentage set by the stake pool operator. In the case of the GOAT pool, we charge 2.5%. Thus 9660 x 2.5%=241.5 ADA.
Delegators will be left with 9660-241.5=9418.5 ADA, distributed to each delegator in proportion to the amount of stake delegated.
Both the fixed fee and the variable fee are only charged when the pool receives a reward. If the pool does not receive a reward in an epoch, the operator does not receive any fee.