IT only Allows Adding 2 Fields at a time so the Solution is to write it in such a way that it considers the addition of the first 2 as a single entity and then adds again
add({add({add({add({add({P0};{P1})};{P2})};{P3})};{P4})};{P5})
This is how the Formula should look like to add all P0 to P5, well i added 6 parameters, in case it should be 5 but yous should get the General Idea.