In case of composite supplies, you need to refer section 8 of CGST Act, 2017.
The tax liability on a composite or a mixed supply shall be determined in the following manner, namely:—
(a) a composite supply comprising two or more supplies, one of which is a principal supply, shall be treated as a supply of such principal supply; and
So, if you supplying a composite supply then you need to charge tax as per principal item you supplied.
For example, charging insurance in tax invoice on goods supplies, the tax rate on insurance charged will be same as tax rate on principal goods you supplied.
You will get full ITC and even recipient or buyer will get full credit subject to if input is allowed for supply.