Hope this might be helpful:
To prevent dimension posting on specific G/L Accounts in Business Central:
- Go to the Chart of Accounts.
- Select your desired G/L Account(s) (e.g., your VAT G/L Accounts).
- After selecting the Account No., go to the navigation menu, select the "Account" tab, then choose "Dimensions - Multiple."

- The Default Dimensions box will appear. Here, you can choose the Dimension Code, Dimension Value Code, and Value Posting. To make the code not mandatory for posting to this G/L Account, select "No Code."

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