No one else has replied to this so I'll make a couple of comments although I'm no expert. I'm quoting from "Pennington's Butterflies of Southern Africa" (1978) ed CGC Dickson & DM Kroon.
Layman Amauris a. albimaculata - "the spots of the forewing are always pure white, whereas in A. echeria they are more often ochraceous. But the best way to distinguish the two is to observe the palpi, which in A. albimaculata have an elongate white stripe, but in A. echeria a white dot."
Chief Amauris e.echeria - "... variable species, ... usually shows ochraceous forewing spots".
After all that I'm undecided about your butterfly. the forewing spots do look pure white (=A. albimaculata) but some of Pennington's photos of A.echeria also show specimens with white spots but this is shown in the inland form vaal and subspecies lobengula His photo of A. e. echeria (the coastal subspecies) does show ochraceous forewing spots but how consistent this is I don't know - thus the comment about variability?
I can't make out the palps on your photo, this feature seems to be the clincher.
I have to say that your photo doesn't exactly match any of the ones in Pennington's, and he has got 5 of the two coastal subspecies, (2 of A.a.a. and 3 of A.e.e). e.g. the three apical spots on the forewing of your photo are more regular than those shown in his photos for either species.
That's the best I can do - I'd guess that it is a Layman but not certain of it.