[magician4]

My sources give pK_a2 as 1.99.

as I said: same ballpark, and doesn't make that big a difference for our discussion
my sources  (sulfuric acid = "Schwefelsäure" : pK_a2 = "pK_S2" )

I tend to disagree. (...)

again, I don't see that there's a real disagreement here: of cause you're right with what you wrote
question is what teoporta by

"..and how to fix such pH value."

would mean,  and what we'll accept to be a buffer

basically, what you say is that at such pH-values a solution usually shouldn't need an additional  pH -fixing at all, as it is already quite  stable all by itself (due to the high H⁺ concentrations involved here, and due to the logarithmic nature of the pH ): and you're right
all I'm saying is that if, for whatever reason , teoporta  wishes to have it more stable still (even at such a low pH) , only these substances would offer additional stability

I can't find the contradiction here


regards

Ingo