Sounds like good old DnD.
...Assuming it was, wouldn't your allies know that the wall was illusory? Like, wouldn't tell them that it was an illusion in some manner that didn't alert the enemies? Especially after they fired through it?
Yep! So the illusion looks real to everyone but if they try to interact with it, it doesn't behave the way they expect (in this case, you could walk right through if you tried). If you disbelieve (use up your round making a saving throw against it) you can see through the illusion as if it were a weak hologram.
The idea is that the goblins, being unsophisticated, would assume the new stone wall was solid and not bother trying to shoot arrows through it or walk through it. Anyone who spent enough time around wizards to know how difficult various spells are, would probably get suspicious that the wizard used a medium level spell in such a lame way. Which means that while they're more likely to try to disbelieve, they might also try to disbelieve some spells that are real.
So the enemies didn't bother trying to fire through. But my party also didn't know what to do. Helvetica doesn't speak a language that only the party understands, so she couldn't tip them off without tipping off the goblins. We worked it out for the future but I was really hoping for a leap on their part. Such as, "hmm, so Helvetica can cast Wall of Stone suddenly?"