Can I add my own tax rate when creating invoices?

SAP Business Network.

You can add a tax or VAT rate that has not been specified by your customer only if your customer allows it (Allow suppliers to create a tax rate and type for invoices and credit memos rule is set to Yes).

To add your own tax rate to the invoice during the invoice creation process:

1. In the Tax section, click the arrow next to Category.
2. In this list, you'll see the values specified by your customer, along with the Other Tax option.
3. Choose Other Tax.
4. Give the category a name and description.
5. Enter the desired rate and taxable amount.

You can also add a tax rate at the line-item level by switching tax to the line level and then following the same steps.

Creating this tax rate doesn't save it to the list of specified values. You need to add the tax rate every time, manually. If you have the Configure Tax Menu option in the list of tax values, you can configure a tax rate and save it. If you are not able to save your tax rate, you can request that your customer add this rate to their list of valid tax values.

You may check the article: How do I view my customer's transaction rules?

SAP Business Network for Procurement & Supply Chain > Transaction Documents > Transaction (Invoicing)