According to the file
FAQ - SnapMirror active sync (SM-as) for ONTAP 9.15.1.pdf
"What are the supported platforms for SnapMirror active sync?
Answer: SM-as supports only two-node HA clusters, either AFF or ASA models. This includes A-Series
and C-Series. Both primary and secondary clusters must be the same type, either AFF or ASA. Protection
for business continuity involving FAS models is not supported."
So I want to know if the primary clusters is AFF C400 and secondary clusters is AFF A300, SM-as supports?