You can't specify player as source of damage when applyDamage method is used on entities.
Code to reproduce:
anyEntity.applyDamage(5,{damagingEntity:mustBePlayer});Error message:
[media]Pack to reproduce available: down below
MCPE-172779
[ScriptAPI] applyDamage -> Player is not valid type in interface EntityApplyDamageOptions
Resolved
Fixed
0
(Unassigned)
1074269
Plausible
Multiple
Windows 11
Script-API
1.20.20.20 Preview
1.20.70
Retrieved
Luckily this is not a bug, you are just missing the non-optional damage cause. e.g.