process is not defined error when calling server function

import testFn from "@/test";

...
const AppContext = createContext<AppContextType | null>(null);

export const AppContextProvider = ({ children }: { children: ReactNode }) => {
  const [userMode, setUserMode] = useState<UserMode | undefined>(undefined);
  const [isMounted, setIsMounted] = useState(false);
  useEffect(() => {
    if (typeof window !== "undefined") {
      const appContextStored = localStorage.getItem(AppContextStorage.STORAGE_KEY);
      if (appContextStored) {
        try {
          const parsed = JSON.parse(appContextStored) as AppContextStorage;
          setUserMode(parsed.userMode);
        } catch (error) {
          testFn();  // CALL SERVER FN
          setUserMode(UserMode.User);
...

import { createServerFn } from "@tanstack/react-start";

const testFn = createServerFn({
  method: "POST",
}).handler(() => {
  console.log("Kepa");
});

export default testFn;

index.js?v=e1735df9:6 Uncaught (in promise) ReferenceError: process is not defined
    at createClientRpc (index.js?v=e1735df9:6:41)
    at test.tsx:1:55

const createClientRpc = (functionId, serverBase) => {
    const sanitizedAppBase = sanitizeBase(process.env.TSS_APP_BASE || "/");