Am I required to pay the €300 application fee even if I don’t receive any offers of admission?

NO. You are required to pay the application fee to CampusArt only if you accept an offer of admission. Once CampusArt receives that payment, you will receive an acknowledgment of your acceptance of the admission offer, a document that you will need to obtain a student visa.
If you do not receive the acknowledgment within three weeks, write to the admissions office at the institution whose offer you accepted.
Send copies of your messages to CampusArt.

Important note: If you accept an offer of admission from a private institution, you will be asked to pay a portion of the program tuition directly to the institution before the institution will issue the acknowledgment of admission. The amount to be paid is specified in the institution’s description on the CampusArt Web site, or on the institution’s Web site.