"Can't promote due to audio copyright issue" Hellp

My latest video isn't getting any views like at all. Last time my vid got a decent amount but this time it's not. I wanted to promote but it wouldn't let me due to "copyright issues". I wanna find some audio to pair with my vid bc it's cooler like that, but idk what's copyrighted and what's not. I mainly think it's why I'm not getting any views at all, but I also just wanna use that feature. BASICALLY how do I check beforehand so I'm not just going through each audio one by one? If there's a way