I will discuss the first 3D-general relativistic magnetohydrodynamic (GRMHD) simulation of sustained accretion onto a horizonless singularity in which matter falls onto the central object rather than being accumulated outside of it or expelled in outflows. We consider a Joshi-Malafarina-Narayan JMN-1 type spacetime, a well-motivated black hole mimicker arising from gravitational collapse with anisotropic pressure in general relativity, with a compactness parameter resulting in a null type central singularity. We find that the simulation reaches a sustained magnetically arrested disk state. For the parameters of the low-luminosity active galactic nucleus system M87* we find the accretion rate of (3-5) x 1e-6 MEdd, fully consistent with the estimates driven by the Kerr GRMHD, and in particular comparable with our reference Schwarzschild black hole simulation. Synthetic raytraced images at 230 GHz, computed through polarized general relativistic radiative transfer, are broadly consistent with the observations of M87* by the Event Horizon Telescope (EHT). We identified a key observational discriminant between a black hole and JMN-1, related to the presence of brightness in the images inside the “shadow” of JMN-1. This brightness is related to emission located very close to the central singularity, in the region that would be blocked by the event horizon in case of a black hole spacetime. Such a signature, while inaccessible to current EHT observations, falls within the projected imaging dynamic range of the near-future radio-interferometric instruments, offering a robust observational test of the black hole paradigm.