Hello,
You confirm the email address for your sandbox account by checking the email sent to the "notifications" section of your PayPal Developer account.
https://developer.paypal.com/docs/integration/paypal-here/sandbox-testing/configuring-accounts/An email address, which does not have to be a working email address, to reference this test account in your API calls and to log in to the PayPal sandbox test site for reviewing account information. The sandbox does not send email messages outside of the sandbox environment.
Note: Email messages from the sandbox environment, to sandbox accounts, resulting from your testing of API requests, are displayed on the PayPal Developer site (Dashboard > Sandbox notifications).
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