Phantom 404 response when persisting data to Mongo

[megaton-neutrino]

The communication flow ends prematurely as my route handler service function persists data to mongo.
app.config.ts
app.use(attachApiResponseObject); app.use("/api", routes)
routes/index.ts
router.use("/users", usersRoutes);
routes/user.routes.ts
router.post("/:id/follow", userService.verifyUserSession, followUser);
controllers/users.controller.ts

export async function followUser(req: Request, res: Response): Promise<void> {
...
try{
...
const updatedUser = await userService.followTargetUser( followerId, targetUserId );
req.apiResponse.success(res,{targetUserId: targetUserId});
} catch (err) {
...
}

services/user.service.ts

async followTargetUser(followerId: string, targetUserId: string): Promise<IUser | null> {
        if(followerId === targetUserId){
            throw new Error("Users cannot follow themselves");
        }

        const followerObjId = new Types.ObjectId(followerId);
        const targetObjId = new Types.ObjectId(targetUserId);

        try {
            const [follower, target] = await Promise.all([
                UserModel.findByIdAndUpdate(
                    followerObjId,
                    { $addToSet: { following: targetObjId }},
                    { new: true}
                ),
                UserModel.findByIdAndUpdate(
                    targetObjId,
                    { $addToSet: { followers: followerObjId }},
                    { new: true }
                )
            ]);

            if (!follower || !target) {
                throw new Error("Either follower or target user not found.");
            }
            return follower;
        } catch (error){
            throw error;
        }
    }

these are the Colyseus logs:

------------------------------ FOLLOW ------------------------------------  

11-09  09:13   [info]:   [UCTRL] POST - /api/users/690d6e00ac7d53845ba8984a/follow  

11-09  09:13   [info]:   [UCTRL] User: {"sessionToken":"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VySWQiOiI2OTBkNmUwMGFjN2Q1Mzg0NWJhODk4NGEiLCJmaXJlYmFzZVVpZCI6ImFneWtJUW5jblFXdDgxQzJqWjJ3VlZVOUpYdDEiLCJlbWFpbCI6ImRAZC5kZCIsImlhdCI6MTc2MjY3OTI4MSwiZXhwIjoxNzYyNjgyODgxLCJpc3MiOiJhcmthZGEtYXV0aC1zZXJ2aWNlIn0.Vq9XTqK-ZY6Mfz6nyeObbzyP-xaklbzX8u2ZBVmwETE","firebaseUid":"agykIQncnQWt81C2jZ2wVVU9JXt1","email":"d@d.dd","userId":"690d6e00ac7d53845ba8984a"}  

11-09  09:13   [info]:   [UCTRL] sessionToken: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VySWQiOiI2OTBkNmUwMGFjN2Q1Mzg0NWJhODk4NGEiLCJmaXJlYmFzZVVpZCI6ImFneWtJUW5jblFXdDgxQzJqWjJ3VlZVOUpYdDEiLCJlbWFpbCI6ImRAZC5kZCIsImlhdCI6MTc2MjY3OTI4MSwiZXhwIjoxNzYyNjgyODgxLCJpc3MiOiJhcmthZGEtYXV0aC1zZXJ2aWNlIn0.Vq9XTqK-ZY6Mfz6nyeObbzyP-xaklbzX8u2ZBVmwETE  

11-09  09:13   [info]:   [UCTRL] route parameter: 690d6e00ac7d53845ba8984a  

11-09  09:13   [info]:   [UCTRL] BODY: {"targetUserId":"690d6dbaac7d53845ba89846"}  

11-09  09:13   [warn]:   [UCTRL] trying to follow user  

11-09  09:13   [warn]:   [MONG FU] inside followUser()  

11-09  09:13   [info]:   [MONG FU] followed obj: "690d6e00ac7d53845ba8984a"  

11-09  09:13   [info]:   [MONG FU] target use obj: "690d6dbaac7d53845ba89846"  

11-09  09:13   [info]:   [MONG FU] trying to persist follow user data  

[404] Unmatched route: POST /api/users/690d6e00ac7d53845ba8984a/follow

[2025-11-09T09:13:39.395Z] Response: 404 for POST /api/users/690d6e00ac7d53845ba8984a/follow


11-09  09:13   [info]:   	[UCTRL] updated user: "{\"_id\":\"690d6e00ac7d53845ba8984a\",\"firebaseUid\":\"agykIQncnQWt81C2jZ2wVVU9JXt1\",\"email\":\"836245acd6218a1cabf310b6:872ec8262a85c69e808c34e679d4bbc0:d8712e5fdd93\",\"email_verified\":false,\"displayName\":\"game-member\",\"sessionToken\":\"New User Registered\",\"role\":\"PLAYER\",\"balance\":330,\"followers\":[],\"following\":[\"690d6d7cac7d53845ba89836\",\"690d6dbaac7d53845ba89846\"],\"createdAt\":\"2025-11-07T03:56:48.242Z\",\"updatedAt\":\"2025-11-09T09:13:39.435Z\",\"emailRaw\":\"d@d.dd\",\"emailHash\":\"2d350321e1f127c850350d48439a38d0b6b5588ef451e0e6bcc50f8035b33b25\",\"__v\":0}"  

11-09  09:13   [info]:   [UCTRL] apiResponse sent response successfully  

11-09  09:13   [warn]:   [UCTRL] in FINALLY  

The entire route executes reaching the endpoint completely. The data is persisted to the db, the apiResponse runs as expected. The problem lies in that Express/Colyseus(???) sends a phantom 404 directly after "const [follower, target] = await Promise.all([..." runs successfully. The subsequesnt req.apiResponse.success has no effect. Why could this be happening?

I can post more code if necessary
thank you