Some add-blockers and antivirus might interfere with the pop-up your bank shows to authorise a payment when using the recommended option of authenticating a payment within Apron, causing the payment to fail.
In order to allow your bank to initiate payments at Apron, you shall whitelist the URL https://app.getapron.com in the admin panel of the browser extension.
If the problem persists, or if your browser does not support whitelisting, you can always use Apron using 'Pay via bank transfer' in the payment method selection screen.