Postman Get request works but not in browser- react/mongoose/express

Question

I know there are a lot of other "works in postman and not in browser" posts, but I've read through them and cannot find anything to give direction on what I'm not catching here. Most of those had to do with proxy issues, but I dont have any proxy's set up.

I recently changed from using a pymongo backend to mongoose/express. My find() works for the get all clients just fine on the browser side, but the findOne() get comes back undefined (I was getting an unexpected token JSON error but that is resolved although I dont know what actually fixed it), yet in Postman it brings exactly what I'm looking for. I'm assuming its something simple, but I can't seem to spot it.

Backend- index.js

const express = require("express")
const mongoose = require("mongoose")
const cors = require('cors')
const clientRoutes = require("./routes/clientRoutes")
const contractRoutes = require("./routes/contractRoutes")
const bodyParser = require('body-parser');

mongoose
    .connect("MONGODB URL", { useNewUrlParser: true })
    .then(() => {
        const app = express()
        app.use(express.json())
        app.use(cors())
        app.use(bodyParser.json());
        app.use("/api", clientRoutes)
        app.use("/api", contractRoutes)

        app.listen(5000, () => {
        console.log("Server has started")   
        })

})

Schema

const mongoose = require("mongoose")

const schema = mongoose.Schema({
    clientId: Number,
    firstName: String,
    lastName: String,
    phone: String,
    contracts: [{
        contractId: Number,
        authNumber: String,
        contType: String,
        contHours: Number,
        contStartDate: Date,
        contEndDate: Date
    }],

})

module.exports = mongoose.model("Client", schema)

routes-

const express = require("express")
const Client = require("../models/Client.js")
const router = express.Router()


//Client routes
router.get("/clients", async (req, res) => {
    const clients = await Client.find()
    res.send(clients)
})

router.get("/clients/:clientId", async (req, res) => {
   try {
    const client = await Client.findOne({ clientId: req.params.clientId })
    res.send(client)
   } catch {
       res.status(404)
       res.send({ error: "Client not found"})
   }
})

React frontend component making the request-

import React from 'react';
import PropTypes from 'prop-types';
import { withRouter } from 'react-router-dom';
import ChartNav from './ChartNav';
import ClientContext from './ClientContext';




class ClientChart extends React.Component {

    

    static get propTypes() {
        return {
            match: PropTypes.any,
            clientId: PropTypes.any
        }
    }

    constructor (props){
        
        super(props);
        this.state = {
            clientId: this.props.match.params.clientId,
            client: {},
            isLoading: true,
            errors: null
        };
        console.log(this.state.clientId)
        
    }
    
    
    componentDidMount(){
        
        fetch(`http://localhost:5000/api/clients/${this.state.clientId}`)
            .then(res => res.json())      
            .then(
                result => {
                    let client = JSON.parse(result.data);

                    this.setState({ 
                        isLoading: false,
                        client: client,
                        
                     });
              }, [])
              .catch(error => this.setState({
                error: error.message,
                isLoading: false,
              }));
              
    }

console and response

404

XHR GET http://localhost:5000/api/clients/undefined

error "Client not found"