[Coinbase Pay SDK] "generateOnRampURL" approach - no callbacks?

Following the integration of Coinbase Pay, you can have more control over the implementation when opting for Generating a URL | Coinbase Cloud approach, where SDK generates proper URL and dapp decides how & where to trigger it.

Thats working fine as per minimal example here (insert your own “appId” key): cbpay-generate-url - CodeSandbox

However according to Generating a URL | Coinbase Cloud - with this approach no callbacks can be passed. How dapp is supposed to know that Coinbase experience has finished / succeeded / cancelled etc?

Can you advise?