We would like to purchase a Monotype font for the use on our websites (.com and .de). Do we need to purchase a lincese for each single domain?

Monotype web fonts are licensed according to the number of “page views”. A license is valid for all domains registered by the licensee. Thus, only one license is required for the websites.

Source:

EULA Monotype Web Fonts (Pay as you go), EULA Monotype Web Fonts (Pay once)