JSFiddle - React, Tailwind, and code Playground

HTML

<form id="formaPagoForm" name="formaPagoForm" method="post" action="">
    Sabadel<input type="radio" name="modoPago" id="sabadell" value="sabadell"><br/>
        Paypal<input type="radio" name="modoPago" id="paypal" value="paypal">
  </form>
<button type="input" onclick="enviar()">IR A PAGAR</button>

<form id="paypalForm" name="paypalForm" method="post" action="">
        <input type="text" name="xxx" id="xxx" value="paypalForm">
</form>
    
<form id="sabadellForm" name="sabadellForm" method="post" action="">
        <input type="text" name="zzz" id="zzz" value="sabadellForm">
</form>

JavaScript

function enviar(){
    if (document.forms.formaPagoForm.paypal.checked==true){
        alert("hola 1");
        document.forms.paypalForm.submit();
    }
else if(document.forms.formaPagoForm.sabadell.checked==true){
    alert("hola 2");
    document.forms.sabadellForm.submit();
    }
}