Seller onboarding is not working due to partner.js giving 503 error

[saasberry]

Hi 

We are using the below method to onboard sellers on our platform

https://developer.paypal.com/docs/multiparty/seller-onboarding/build-onboarding/ 

where https://www.sandbox.paypal.com/webapps/merchantboarding/js/lib/lightbox/partner.js  this js being used is not which is not working now its giving 503 error due to that our seller onboarding process is not working 

for ref added source code 

<script>
  function onboardedCallback(authCode, sharedId) {
    fetch('/seller-server/login-seller', {
      method: 'POST',
      headers: {
        'content-type': 'application/json'
      },
      body: JSON.stringify({
        authCode: authCode,
        sharedId: sharedId
      })
    }).then(function(res) {
      if (!res.ok) {
        alert("Something went wrong!");
      }
    });
  }
</script>
<a target="_blank" data-paypal-onboard-complete="onboardedCallback" href="<Action-URL>&displayMode=minibrowser" data-paypal-button="true">Sign up for PayPal</a>
<script id="paypal-js" src="https://www.sandbox.paypal.com/webapps/merchantboarding/js/lib/lightbox/partner.js"></script>