It's my pleasure to help you fix the error message when connecting your Santander account in QuickBooks.
Are you using the QuickBooks Online mobile app to connect your Santander account? The error message is likely caused by an outdated app, or there's an issue within the app itself.
In this case, we'll want to make sure that the mobile app is updated to the latest version. Open Google Play or Apple App Store (For iOS), then search for the mobile app. When prompted, tap the Update button.
After updating, connect your account again. If you're still getting the error, let's uninstall, then reinstall the app to fix the issue.
Alternatively. we can use a browser to connect the Santander account.
However, if you're using a browser, let's check to see if this is caused by a cache-related issue. When a browser's cache is full or corrupted, issues like this would become more common.
Let's rule this out by using an incognito or private window:
Google Chrome: Press CTRL + Shift + N.
Safari: Press Command + Shift + N.
Mozilla Firefox or Microsoft Edge: CTRL + Shift + P.
Log in to QuickBooks, then connect your account. When you're able to do so, let's go back to the regular browser and clear the cache.
After following the prompts, close out any browser processes, then re-open your preferred browser so you can work on your books.