Nginx location block for wordpress and legacy files

Hi . I am trying to serve legacy html website documents from the new site which is a wordpress site.

The new site is using nginx and I want to be able to serve files which are structured with a permalink like /articles/file-uri and the 10 years of legacy html static files from a directory in the root called legacy.

I have had some success with these blocks :

index index.php;
location ^~ / {
root /var/www/mysite.com/htdocs;
                try_files $uri /legacy/$uri $uri/ @fallback;
}

location @fallback {
root /var/www/mysite.com/htdocs;
try_files $uri $uri/ /index.php$args; 
}

However the uri http://mysite.com/ results in the index.php being forced as a download of text.

I do not see why the index.php file is being sent as application/octet-stream.

thank you for any help that you might provide.