Astrometric (right ascension, α, and declination, δ, top two panels) and spectroscopic (LOS velocity, bottom panel) impact of considering a PPN parameter, β ≠ 1, for different values of percentage deviation from unity, for the S2 star. The horizontal dotted lines correspond to the nominal accuracy of the GRAVITY interferometer and the SINFONI spectrographer, for astrometric and spectroscopic observables, respectively.