redshift ($z$) so that one can only measure from GW signals the redshifted mass $m(1+z)$ [@schutz86]. In two astrophysical scenarios, the mass-redshift degeneracy could lead to an significant overestimation of the masses of BBHs. In the first scenario, a BBH is at a high cosmological redshift and, nevertheless, is detected because the GW signal is magnified due to gravitational lensing [@broadhurst18; @smith18]. So far, there is no convincing evidence supporting this scenario [@hannuksela19]. This scenario also has difficulties explaining the positive correlation between the apparent masses and distances of the detected BBHs [@ligo18a]. In the second scenario, the BBH is captured by a supermassive black hole (SMBH) to a small distance, so that Doppler and gravitational redshifts become significant, which then lead to the mass-redshift degeneracy [@chen_han_2018; @chen19]. The uncertainty of this latter scenario lies mainly in the poor understanding of the event rate. In both scenarios the signal in the LIGO/Virgo band (centered around $10-10^2$ Hz) is similar to that of a not-redshifted, but more massive BBH. Distinguishing them would be difficult partly because the signal is short, which normally lasts no more than one second, too short to reveal any signature of gravitational lensing [@hannuksela19] or a nearby 