Аннотация:MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 210430B ( Fermi GBM team, GCN 29916) errorbox 6673 sec after notice time and 6710 sec after trigger time at 2021-04-30 23:34:08 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 79 deg. The sun altitude is -23.0 deg. The galactic latitude b = -47 deg., longitude l = 86 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1604728 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________| _____________________|__________ ___________|_____________________ _______________|_____|_______|___ ____|________ 6741 | 2021-04-30 23:34:08 | MASTER- Kislovodsk | (22h 47m 52.89s , +14d 03m 13.2s) | C | 60 | 16.9 | 6741 | 2021-04-30 23:34:08 | MASTER-Kislovodsk | (22h 51m 45.19s , +13d 39m 00.0s) | C | 60 | 17.1 | 6901 | 2021-04-30 23:36:49 | MASTER-Kislovodsk | (22h 43m 52.25s , +10d 04m 18.5s) | C | 60 | 16.9 | 6901 | 2021-04-30 23:36:49 | MASTER-Kislovodsk | (22h 47m 40.74s , +09d 40m 01.6s) | C | 60 | 16.9 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.