What is the difference between tax included vs tax excluded?
Tax Included means that you sell a service/product at the same price for all customers at all times in all countries.
The excluded tax amount will be all time the same, 100€ for instance. And the taxes will be calculated before the payments during the checkout and added to the excluded tax price depending on your customer evidence (Business or Consumer, Billing Country, IP address, Credit card country), your tax threshold and the nature of the item sold.