The problem is not this a318 , there was a old A318 in workshop with steam id -1 , and if a airline (mostly old ones) have a -1 steam id as needed planes you get that warning. I not would use airlines older then 2018 , then you not have that issue. To fix that issue at you , you need to look in the configs if your old mairline mods if there is somewhere a -1 steam id , just change that to 0 or delete that and it will work.

have the same issue and I did what you said and it didnt fix the glitch. How do I fix it?

if you need more help , please come to Sim Airport Discord (link is in SA steam discussion)

That is a steam bug , you must unscubscribe it and subscribe it again (with SA closed) , sometimes you need to do it 2-3x . The mod works , also all my airlines. But that steam bug happens from time to time at different mods. Always subscribe and wait then until it is downloaded.

I am gettin( aircraft config) airbus318 it will not download, I only have you mods, do you which airline had this crazy file inside? How do I get rid of it as it will not download.