Stupid Strigoi

So I finally gave in and bought some of the keys to battle Strigoi and then I used 30 weapons and now it won't let me invite anyone to join my battle?! What kind of bull is that?!? I am so freaking pissed now!
Can someone please explain to me why this happened?! And how is it fair?!

Battles are meant to be fought with others. Generally unless you use the best weapons continually, you will not be able to finsih a battle by yourself. You can invite firned up until a cetain amount of. Damage has been done and friends can only join if a certain amount of damage is remaining. Once you get to around 30-40% damage remaining you need to be careful that you dont lock others out.

Thank u for ur reply! I do know we need to join each other in battles, i have done it before..
It's just that this is the first time it won't let me invite friends!
But the same thing happened again during another boss battle, I invited a couple of friends, used my weapons and then the invite friends button went all brown again!
That's not fair

Once you're about 75% of the way through the battle, you can no longer invite friends. Most of us, like you, have learned this the hard way, so you're in a popular club.

Ya it sucks! Thank u