You need to unlock the other biome by completing one of the contracts.
I waited 4 ingame days after doing said contract but still nothing.
Is there a way to remove clients, have a few that I can't use in any way and just take up space. Accidently gave the wrong serum to one, then tried giving the client the serum for a correct contract but they became unusable in any future contracts. Also once you give someone the chicken serum they become unusable clients as well. (Which I did see your reply to someone else about chickens.)