Hi,
Please refer to notice 741a regarding the place of supply of services:
Place of supply of services (VAT Notice 741A) Section 6 provides guidance on the general rules
The B2B general rule for supplies of services is that the supply is made where the customer belongs.
Section 6.4 lists exceptions to the general rule that you need to check to see if any apply to your situation.
If you determine the place of your supply is not in the UK, then the supply would be outside the scope of UK VAT.
You may also wish to look at notice 700 sections 22 to 25 as these provide guidance on invoicing when acting as an agent:
Supplies made by or through agents
Thankyou.