Validity of my results - Gravity model of Trade - Difference-in-Hansen tests of exogeneity missing''

[PANOS TSITSOGLOU]

A dynamic panel data of 73 countries and 20 years. I am estimating my regression equation using the system-GMM command, however the Difference-in-Hansen tests of exogeneity of instrument subsets are missing. Is my model valid? ΑR(1), AR(2), SARGAN and Hansen Tests are good.

[PANOS TSITSOGLOU]

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[PANOS TSITSOGLOU]

OUTPUT in orger to be more clear

xtabond2 ln_exports_Gr l.ln_exports_Gr ln_im_GDP ln_dis landlocked ISLAND EU Total_Repres lpol_rescale, gmm (l.ln_exports_Gr, lag(1 3) eq (level) collapse) iv(ln_im_GDP ln_dis landlocked ISLAND EU Total_Repres lpol_rescale) twostep robust small



Group variable: unit_id Number of obs = 1386
Time variable : YEAR Number of groups = 73
Number of instruments = 11 Obs per group: min = 18
F(8, 72) = 58017.72 avg = 18.99
Prob > F = 0.000 max = 19

ln_exports_Gr | Coefficient std. err. t P>|t| [95% conf. interval]
--------------+----------------------------------------------------------------
ln_exports_Gr |
L1. | .7396466 .0644743 11.47 0.000 .6111194 .8681738
|
ln_im_GDP | .0706048 .0426523 1.66 0.102 -.0144209 .1556306
ln_dis | -.2658212 .0861373 -3.09 0.003 -.4375328 -.0941096
landlocked | -.3144982 .1079165 -2.91 0.005 -.5296258 -.0993706
ISLAND | .0638789 .1359399 0.47 0.640 -.2071123 .3348702
EU | .0657576 .0815339 0.81 0.423 -.0967772 .2282925
Total_Repres | .0536951 .0239342 2.24 0.028 .0059832 .101407
lpol_rescale | .1888407 .0738037 2.56 0.013 .0417158 .3359656
_cons | 2.551901 .9114989 2.80 0.007 .734861 4.368941

Arellano-Bond test for AR(1) in first differences: z = -4.14 Pr > z = 0.000
Arellano-Bond test for AR(2) in first differences: z = 0.64 Pr > z = 0.525
------------------------------------------------------------------------------
Sargan test of overid. restrictions: chi2(2) = 3.43 Prob > chi2 = 0.180
(Not robust, but not weakened by many instruments.)
Hansen test of overid. restrictions: chi2(2) = 1.83 Prob > chi2 = 0.401
(Robust, but weakened by many instruments.)