In this article we can find only certain summary of the mass-gap problem that is already solved within the Scale-Symmetric Theory (SST). We cannot solve the Yang-Mills mass-gap problem within the quantum Yang-Mills theory because it is incomplete i.e. this theory does not lead to the internal structure of bare baryons (of the core of baryons) that is responsible for production of the massive carriers of the nuclear weak and strong interactions. To solve the mass-gap problem we must describe following three mechanisms: the real Higgs mechanism i.e. we must show how the Einstein-spacetime components (i.e. the neutrino-antineutrino pairs) acquire their gravitational mass because of their interactions with the non-gravitating superluminal Higgs field - it follows from the succeeding phase transitions of the Higgs field described within SST, the mechanism of production of the condensates composed of the neutrino-antineutrino pairs that are responsible for the nuclear weak interactions, and the mechanism of production of the pions that are responsible for the nuclear strong interactions of baryons. Such mechanisms are described within SST which is the mathematically coherent theory.