What's a good rev split btwn indie dev / app publisher?

Hi guys,

I have developed a mobile app that generates good revenue. But the market is highly competitive and as an indie developer, it's hard to correctly optimize the ASA / ASO. Rev starts to decline.

Therefore I got in contact with an app publishing company that is interested. What should be the rev net split between me and the app publisher? I mean, when should I say no? Is 40% me, 60% them correct?

Thanks!