The SameBookie notice is displayed when selecting an arb where two or more outcomes in an arb is on the same bookmaker.
It is not recommended to place two bets on the same match on the same bookmaker, as this might flag you as a sharp bettor or arber in the bookmakers point of view. Avoid this and your bookmaker accounts will probably last longer!
Please note that this is not a problem with non-limiting bookmakers, like Pinnacle, Betfair, Betdaq and Smarkets. You can bet 2/3 outcomes at these bookmakers.