Why does my QB not connect to HMRC

There are several reasons why this is happening and I'm here to enumerate them and help get you back to business, pjlighthaulage.

You'll have to make sure that you have signed up for the Making Tax Digital (MTD) feature so you'll be able to submit using the new method. However, if you just signed up and are not set up on HMRC yet, wait for a confirmation email before using the new platform.

But if you have already used this method before, you may have used incorrect login credentials. Please know that HMRC authorisation is not MTD specific and will accept any credentials.

In case you didn't authorise QuickBooks to interact with HRMC, you can follow the steps in this article. 

For your reference, here are the most frequently asked questions that you'll encounter when submitting your VAT return: How To Unfile My VAT return when I Have Already Submitted.

Keep in touch if you still experience issues connecting to HMRC. I'll be here to assist you further. Stay safe starting this new year!