When i try and connect my barclays account to quickbooks it is saying the details do not match. I am then getting error code 1521 when trying to unlock my account.

Let's resolve the error you're having to connect the bank successfully, @envv89-gmail-com.

If you're connecting for the first time, be sure to select the right bank and enter your bank sign-in information correctly.

Here's how:

1. From the Banking menu, click on the Add Account field.
2. Enter the bank's URL (for example: https://www.bank.com). If you see multiple options, you may have to repeat these steps to find the correct one. 
3. Provide your sign-in information on your online banking account and then select Continue.

You can check this article for more information: Enhanced Standard Feed Connection Errors.

In the meantime, you can manually download the transactions from the bank and then upload the file to your account. Check this article for more information: Manually upload transactions into QuickBooks Online. 

From here, you can now categorise and then reconcile the transactions.

Let me know if there’s anything else that I can assist with about your bank account by leaving a comment below. I’m always here to assist. Have a wonderful day!