Bookinglayer calculates the VAT excluding it from the gross sum.
Here you can see a VAT formula explanation and an example from the website vatcalconline:

Excluding VAT from gross sum:
VAT calculation formula for VAT exclusion is the following: to calculate VAT having the gross amount you should divide the gross amount by 1 + VAT percentage (i.e. if it is 15%, then you should divide by 1.15), then subtract the gross amount, multiply by 1 and round to the closest value (including eurocents). The last two operations are not mandatory since you see the VAT value even before you do them.
Example:
1. Imagine you charge 20eur for an accommodation and the VAT rate is set to 21%.
2. In the booking's invoice, you will see the VAT breakdown (in case you have opted to show the VAT breakdown in your invoices  article)
3. According to the VAT exclusion formula, the correct VAT amount for a total of 25 EUR is 4.34 EUR.