Cant assign an argument of type 'X' to parameter of type 'X'

Im receiving a parameter, that can be an array that contain many literal objects or an literal object directly.

This is the method:

public add(optionsStack: RTypes.RouteParam): this {

        if (Array.isArray(optionsStack)) {
            optionsStack.forEach((routeItem: RTypes.Route) => {
                // Check if any property wasn't gived
                ok(routeItem.path);
                ok(routeItem.method);
                ok(routeItem.requestHandler);

                // Covering problem that may exist
                routeItem.method = routeItem.method.toUpperCase();

                this.routes.push(routeItem);
            });
        };

        if (Object.getPrototypeOf(optionsStack) === Object.prototype) {
            ok(optionsStack.path);
            ok(optionsStack.method);
            ok(optionsStack.requestHandler);
    
            // Covering problem that may exist
            optionsStack.method = optionsStack.method.toUpperCase();
    
            this.routes.push(optionsStack);
        };
        
        return this;

When I give an array with objects, the function works as I expect here:

I have delete the part that check only for literal objects to show this console.log (In that part is the error)

router.add([
    {
        path: "/",
        method: "get",
        requestHandler: ((req, res) => {
            res.end("<h1>Hello World!</h1>");
        })
    },
    {
        path: "/about",
        method: "get",
        requestHandler: ((req, res) => {
            res.end("<h1>Hello World from About Page!</h1>");
        })
    },
])

Terminal output:

HRouter {
  routes: [
    {
      path: '/',
      method: 'GET',
      requestHandler: [Function: requestHandler]
    },
    {
      path: '/about',
      method: 'GET',
      requestHandler: [Function: requestHandler]
    }
  ]
}

But in the method I get some errors, like:

The property 'path' dont exist on type 'RouteParam'
The property 'path' dont exist on type 'Route[]'

The property 'method' dont exist on type 'RouteParam'
The property 'method' dont exist on type 'Route[]'

The property 'requestHandler' dont exist on type 'RouteParam'
The property 'requestHandler' dont exist on type 'Route[]'

Can not assign an argument of type "RouteParam" to parameter of type "Route"
The type "Route" is missing the following properties from type "Route": path, method, requestHandler

And here is the types used in the method:

import { RequestListener } from "node:http"

export interface Route {
    path: string;
    method: string;
    requestHandler: RequestListener;
};

export type RouteParam = Route | Route[]

How I can fix it?. Thanks :)