Https://uk.selfemployed.intuit.com/login?realmId=9130351703123296&from=qboaWhen opening my clients QuickBooks online I get HTTP Status 400 - Bad Request

I know having this problem can be time-consuming, especially when you try to open your client's account in QuickBooks Self-Employed (QBSE), Oliver. Let me help you with your concern.

Error 400 typically indicates that the server cannot process the request due to a perceived issue, often related to corruption. If you're attempting to connect to your bank, we can take some steps to identify the problem. Start by logging into your bank's website to see if the same error occurs. If it does, the issue might be on your bank's end. In that case, consider contacting them for further investigation.

On the other hand, you can try manually updating your bank account to refresh the connection between QuickBooks and your financial institution.

1. Go to Transactions and select Bank Transactions.
2. Select Connect account. After clicking your bank, then select Let’s Go.
3. Read through the terms and conditions, then select Agree.
4. Choose Sign in and enter your online banking credentials. Then, follow the steps to connect to your bank. Your bank may require additional security checks and may take a few minutes to connect.
5. Click the account you want to share with QuickBooks, such as savings, current, or credit card.
6. Select the date to start pulling transactions into QuickBooks. Then select Connect, and then Done.

I'm also adding this article for your reference about fixing banking errors in QuickBooks.

If there's anything else you need help with logging into your client's account in QuickBooks, let me know by adding a comment. I'm always here for you. Have a good day!