It is not possible to call an Airtable webhook from a button field set to open.a url. Airtable webhooks only work with POST requests, but the open url action sends a GET request. It is possible to have a button field call a script, and then have that script call the webhook.
On the other hand, can you explain why you want to launch an Airtable webhook from a button field? An Airtable webhook runs an Airtable automation. However, if the user can run a button script in Airtable, there are easier ways to trigger the automation, assuming that the automation is in the same base. If they are different bases, then the base receiving the webhook won’t have access to the record with the id you sent.