How can I enter a company name and VAT number on the invoice?

You can enter your data or the data of your band directly in the checkout process in step 4 via the “Add VAT number” link (all data is mandatory):

If you enter the VAT number (and other company details) directly during the checkout process, sales tax will no longer be shown.

Alternatively, you can also enter the company details on the invoice retrospectively (but then the sales tax will still be shown on the invoice):