Please how do I include VAT line whose calculation and rate is different from all that is available in QBO?

I'll share what I know about this, @oko-selby-gmail-. 

The VAT reverse charge is at its simplest a mechanism where the liability to account for and pay VAT on cross-border services is transferred from the supplier to the receiver of certain services. I'd recommend contacting your state agency to know more about the difference between the two sales tax codes.

Once you've confirmed their difference, we can always go back to QuickBooks Online and set up the sales tax codes correctly. You can also use these links for reference: 

• How do I set up sales GST/VAT rates and use them on forms? (International QBO)
• Edit sales tax rate in QuickBooks Online

There's also an option where you can add a custom VAT rate for purchases in QuickBooks Online. Here's how:

1. Go to the Taxes menu, then click Add tax in the upper-right hand corner.
2. Click Tax rate or Custom tax.
3. Enter the Tax name, Description of the tax, and the Tax agency that collects the tax.
4. Check the box for Purchases.
5. Enter the VAT rate and account where the tax is reported, then provide all other required details.
6. Click Save.

We always want to ensure we're compliant with Ireland's rules and regulations. Thus, visit their website for more information: VAT Rates Overview. 

Lastly, you can check out our resource hub to get links about managing your tax-related tasks in QBO. 

The Community is always here if you need anything else.