If one variant of the same bank works, and other variant of the same bank not works solely based on BIN.
Bank provided certain BIN numbers to Instamart (ex: provide this offer if card having first 6 digits as 555555), those are related to specific variant or network in that bank. If it didn't match then Instamart says 'this card not allowed', which indirectly means 'bank provided bin not matched with your bin'.
Btw, BIN = First 6 digits.