  We show that using renormalization-group summation to generate the QCD
radiative corrections to the $\pi-\gamma$ transition form factor, calculated
with lightcone sum rules (LCSR), renders the strong coupling free of Landau
singularities while preserving the QCD form-factor asymptotics. This enables a
reliable applicability of the LCSR method to momenta well below 1 GeV$^2$. This
way, one can use the new preliminary BESIII data with unprecedented accuracy
below 1.5 GeV$^2$ to fine tune the prefactor of the twist-six contribution.
Using a combined fit to all available data below 3.1 GeV$^2$, we are able to
determine all nonperturbative scale parameters and a few Gegenbauer
coefficients entering the calculation of the form factor. Employing these
ingredients, we determine a pion distribution amplitude with conformal
coefficients $(b_2,b_4)$ that agree at the $1\sigma$ level with the data for
$Q^2 \leqslant 3.1$ GeV$^2$ and fulfill at the same time the lattice
constraints on $b_2$ at N$^3$LO together with the constraints from QCD sum
rules with nonlocal condensates.The form-factor prediction calculated herewith
reproduces the data below 1 GeV$^2$ significantly better than analogous
predictions based on a fixed-order power-series expansion in the strong
coupling constant.
