Banking primary user changed (HSBC Business). Tried to update banking connection but failed, error message each time, saying 'unable to complete request' when logging in

Thanks for providing details of your concern, @chesterfordspres. I understand the impact of any delay in resolving this recurring connectivity issue with your HSBC bank account. Don't worry, I'll share some troubleshooting steps to fix this.

First, open your QuickBooks Online account using an incognito window and connect the bank from there. The incognito mode does not save any history, which makes it a great place to identify issues in the browser. You can also use other supported browsers for the best experience when using QuickBooks. Utilise these shortcut keys to access a private window:
 

• Mozilla Firefox: CTRL + Shift + P
• Microsoft Edge: CTRL + Shift + N
• Google Chrome: CTRL + Shift + N
• Safari: Command + Shift + N

Once you're in incognito mode, connect your online bank in QuickBooks once again and see if it works without errors. If you already tried this, and still getting the same problem, I recommend getting in touch with our Support Team. They can help report this to our engineers who deal with program bugs and other technical concerns. You can follow the steps highlighted from this link: QuickBooks Online Support.

Moreover, I don’t want to leave you empty-handed. In the meantime, you can download your transactions from your bank's website manually and import them using a CSV file. You can refer to this article that details the process: Import bank transactions using Excel CSV files.

Keep me posted about the result or if you have other QuickBooks concerns. The Community team has your back.