Technically it is
H
2A
+ HA
A
-with pKa1 = 2.4 and pKa2 = 4.9 (more or less, according to the paper you listed, 0.1 error is not that important here).
At pH 7 we are far to the right with the second equilibrium, and [itex]\frac {[A^-]} {[HA]} \approx 10^{7-4.9}[/itex] (concentration of H
2A
+ is negligible).