In accounting, there is no distinction between sales invoices for goods or services. So it is not relevant to speak of service invoices. The only differences between your examples are that tax rates are different and withholding rates are different. Every line item on a sales invoice (whether for goods or services) can have a different tax code with a different rate. But for withholding tax you have only two choices:
- A percentage of the entire amount, including all taxes, or
- A fixed amount.
If you have different withholding rates for different line items, you will have to use the second option and calculate the amount manually. Explain your calculation in the Notes. Some day, things might be different. Right now, you have no other option.