Redirecting expired domains issue

I've been scouring expired domains in my niche, buying them, and redirecting to a specific page on my site.

Never tried this strategy, but i'm running into trouble. Ahrefs is picking up the backlinks being redirected to my site, but they are pointing to pages that don't exist.

For example:

I'm trying to redirect the entire old website to the page: http://www.newsite.com/newsitecontent

I'm seeing some pages from the old site that are being redirected, like this: http://www.oldsite.com/oldsitecontent

Instead of redirecting all old site pages to the single new site page, (http://www.newsite.com/newsitecontent) this is happening:

http://www.newsite.com/newsitecontent/oldsitecontent

I set up the redirects through namecheap, and they are permanent 301. I can't figure out how to make it work.

Anyone know how to solve this without setting up multiple redirect chains?