Universal remote one-for-all -need code for Magnasonic DVD 816-4C

First, you have to realize that there is no 'universal' remote; the description is a fraud. Even the type of remote that can 'learn' codes from an original cannot learn from some of them (we own one like that). They are, at best, 'multibrand' or 'multidevice' remotes.
About the only chance you might have is to check the All-In-One website for an updated list but it is unlikely that all functions of your DVD will be available with that remote.
You may be forced to buy an original remote here:
Remotes
I did not, however, see one for your 816C; only 'B.'