UNABLE TO ENTER MY MONTHLY VAT.

I can share some help to fix this, samuelhallen. 

Before we begin, may I know where did you enter your VAT number and have you encountered any issues as you enter them? This way, we can provide further information to fix this matter. 

In the meantime, we can use a private browser to rule out any browsing history or cached files causing the problem. Here are the shortcut keys for accessing private browsers:

1. Google Chrome: press Ctrl + Shift + N
2. Mozilla Firefox: press Ctrl + Shift + P
3. Microsoft Edge: press Ctrl + Shift + N
4. Safari: press Command + Shift + N 

It's also best to clear your browser's cache and cookies or use other supported web browsers to identify if this is related to your current browser. 

When you're ready, you can utilize this article to submit your VAT electronically: Submit a VAT return to HMRC using MTD in QuickBooks Online. 
 

Please let me know how it goes as you followed the steps above, samuelhallen. We'll be around to assist you further.