Trying to get createdAt

good day seniors, I am new to contentful and I am trying to change my query from getting the publishedAt to createdAt but it gives me this error that says “order” has invalid value sys_createdAt_DESC. Hope you guys can help me. here’s my query:

query($locale: String) {
articleCollection(order: sys_publishedAt_DESC, limit: 8, locale: $locale)