Without seeing all your config, it’s hard to give you specific advice. All I can say is to review carefully the documentation and make sure you have everything in order:
I’m pretty sure you’d have to do that outside Grav in your .htaccess or other server config file. A standard Grav server config will intercept *.php paths, so you’d need them to find your redirects before they reach Grav’s settings. I’m 90% sure
And congratulations on behalf of all web users for taking the trouble to redirect! Not even some of the giant wealthy sites like Google and Microsoft bother with this important step. I see dead links to their old URL schemes a lot, even from within their own sites.