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You can do this by going to Banking > Add account and search for Santander - there should be an option for a personal account in the list.
Thanks for getting back to us, @kimhadley1.
We haven't received any reported cases similar to this. As an initial troubleshooting step, try logging into your QuickBooks Online (QBO) account using a private browser (incognito mode). There are times that the browser is full of frequently accessed page resources, thus causing some unusual responses.
Once logged in, try to connect your bank again:
1. Go back to the Banking menu at the pane.
2. Click Add account and search for Santander.
3. Enter your login credentials, then Continue.
4. Once done, hit Agree and Connect.
If it works, return to your default browser and perform clear cache. Every so often the cache becomes overwhelmed with older data which can potentially cause viewing and performance issues. Clearing it will refresh the system, and you'll be able to work with a clean slate. If it doesn't, try using a different browser to double-check.
For additional resources, consider checking out these articles:
Please let me know if you have any other issues in the comments. I want to make sure everything is taken care of for you.