How to get the back-end request page API client from the front-end request

the back end of the call Mollie API client request payment page written in express is localhost:8000
enter URLlocalhost:8000/api?issuer=ideal_ABNANL2A to jump directly to the payment page using the selected bank.

Front end is localhost:3000 package.json existing proxy
request for backend / api with axios get has no response. Why can I enter URL directly with backend?
the backend code is as follows

  app.get("/api", (req, res) => {

  console.log(req.query.issuer)
   let selectedIssuer =req.query.issuer;

   if (!selectedIssuer) {
   console.log("No selected bank Issuer")
   return
     }



 const orderId = new Date().getTime();

  // After which you can create an iDEAL payment with the selected issuer.
  mollieClient.payments
    .create({
  amount: { value: "10.00", currency: "EUR" },
  description: "Test payment",
  redirectUrl: `https://example.org/redirect?orderId=${orderId}`,
  webhookUrl: `http://example.org/webhook?orderId=${orderId}`,
  metadata: { orderId },
  method: "ideal",
  issuer: selectedIssuer,
})
.then(payment => {
  // Redirect the consumer to complete the payment using `payment.getPaymentUrl()`.
  res.redirect(payment.getPaymentUrl());
   

})
.catch(error => {
  // Do some proper error handling.
  res.send(error);
});
});

the front-end code is as follows

        class App extends Component {
          
        
          handleSend=()=>{
            const obj=document.getElementById("issuer");
            const index=obj.selectedIndex; //
            const val = obj.options[index].text;
        
            axios.get("/api",{
              params:{
                issuer:val }
            }
             
            )
            
          
        }
          render() {
            
          
            return (
              <div>
               Hallo world
               <form >
                <select 
                  id= "issuer"
                  name = "issuer">
                <option value="ideal_ABNANL2A">ABN AMRO</option>
                <option value="ideal_ASNBNL21">ASN Bank</option>
                <option value="ideal_BUNQNL2A">bunq</option>
                <option value="ideal_INGBNL2A">ING</option>
                <option value="ideal_KNABNL2H">Knab</option>
                <option value="ideal_MOYONL21">Moneyou</option>
                <option value="ideal_RABONL2U">Rabobank</option>
                <option value="ideal_RBRBNL21">RegioBank</option>
                
                </select>
                <button onClick={this.handleSend}>Select issuer</button>
                </form> 
                  
              </div>
              
            );
          }
        }