You're within the closing date window. If you're sure you want to make this change, select Save. (code: "INDIRECTTAX-10623")Can you explain this message please??

Hello, shamrock. 

Usually, the date set in the close book window leads to the error code that you've encountered. To avoid receiving an error message when you submit your VAT return, let's review the settings and make sure that no date has been entered in the close the book function.
 

1. Go to the Cog wheel. 
2. Click Account & Settings. 
3. Press Advanced, and check if there is a date entered under the close the books section.  

If a date has been entered, please remove it and disable the close the books function. Once turned off, go ahead and resubmit your VAT return in QBO. 

Please check this link for more details about submitting a VAT return: How to submit a VAT return to HMRC - MTD for QuickBooks Online. 

However, if the issue persists and you keep getting the same error, I'd suggest reaching out to our Customer Care Support. They have the resources to access your account and can start a screen-sharing session and check this further. 

I just want you to know that QuickBooks Community is always here to assist you. So please let me know how it goes by leaving a reply below or if you need more help from me. Cheers!