Include Saleor base URL in externalUrl to pass Saleor request validation

[wcislo-saleor]

If base URL is not included then Saleor responds with a following error.

(data excerpt)

{
	"amount": {
		"amount": 2.0
	},
	"createdAt": "2025-08-06T06:56:21.016053+00:00",
	"type": "CHARGE_FAILURE",
	"pspReference": "",
	"message": "Incorrect value (/dashboard/apps/QXBwOjE1/app/app/transactions/VHJhbnNhY3Rpb25JdGVtOmMzZjQ2N2EwLTk5NzYtNGE1OS04MDFjLTRkODFmYThjOTQ2MQ==) for field: externalUrl. Error: Input should be a valid URL, relative URL without a base."
},

Validation in Core: https://github.com/saleor/saleor/blob/8eb11da07f09437374cb82daa6f10a80a11a1c90/saleor/webhook/response_schemas/transaction.py#L141-L148.

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
dummy-payment-app	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 6, 2025 7:00am

[wcislo-saleor]

#57 is already supposed to fix this.