You may have received a suction cup with a missing/undersized/partly blocked inner hole. Don’t worry, this is an easy fix.
Simply remove the rubber suction cup from the attachment, and use a hex key (some came included in your kit) to break the thin barrier.
Alternatively, you may have forgotten to connect the air pump tube to the intake valve on the suction cup (it happens to us all the time).
Let us know if it helped