Could be a plethora of issues.
Is it in semi mode and not some ramp~"ish" mode?
Ball quality..I looked at the spec and even rated @ 8 bps a graviy fed hopper will not suffice.
Are the eyes on or off?
Basicaly if the eyes are on and there are no issues the marker will fire if a ball is present.
If the eyes are off the marker will fire regardless,combine this with a wet ball which drags due to the friction and the marker will fire even if the balls only half feed into the hopper=
soup...
Read the manual,undertsand the settings,clean the marker,change the battery and try it.
TBH if it fires ok slowly then as said the issue will prolly be the feed rate of the hopper.
Go to the classifieds and get an egg..£20 and useable "when" you upgrade..if your playing seriously you won't have that marker long,it compares to site guns but still good VFM if you sort it....