  We report on MASTER optical observations of an afterglow-like optical and
X-ray transient AT2021lfa/ZTF21aayokph. We detected the initial steady
brightening of the transient at 7{\sigma} confidence level. This allowed us to
use smooth optical self-similar emission of GRBs model to constrain the
explosion time to better than 14 min as well as to estimate its initial Lorentz
factor {\Gamma}0 = 20 +/- 10. Taking into consideration the low {\Gamma}0 and
non-detection in gamma-rays, we classify this transient as the first failed GRB
afterglow.
