Yes, you will need to manually add the permission to the manifest - one way is to modify AndroidManifest.template.xml to add:
<uses-permission android:name="android.permission.POST_NOTIFICATIONS"/>
A suitable location would be just below <%uses-permission%>
You will also need to request the permission in your code, e.g:
PermissionsService.RequestPermissions(['android.permission.POST_NOTIFICATIONS'],
procedure(const APermissions: TClassicStringDynArray; const AGrantResults: TClassicPermissionStatusDynArray)
begin
if AGrantResults[0] = TPermissionStatus.Granted then
// Permission was granted
end
);