Hey, not sure if this is solved, but I found this post that helped me. I had to struggle for the longest time trying to get all the posts within my old blog to the new domain name.
At first, only the main domain worked, then I inserted this code at the top below the rewrite engine, and it worked. It redirects all my posts as well.
RewriteEngine on
RewriteRule ^(.*)$ https://yourcodegarage.com/blog/$1 [R=301,L]
Reference: https://codegarage.com/blog/2011/03/how-to-301-redirect-your-wordpress-blog-to-a-new-url/
