I finally got it to work by running:
fauna upload-graphql-schema fauna/schema.graphql \
--domain db.us.fauna.com \
--secret asdasd \
--mode override \
--graphqlHost graphql.us.fauna.com \
--scheme https \
--graphqlPort 443
notice how I had to provide all options which were supposed to be optional – which I think is a bug.
PS: DON’T USE --method override
!! IT WILL CLEAR ALL RECORDS IN ALL YOUR COLLECTIONS, IT’S ESSENTIALLY THE SAME AS STARTING FROM SCRATCH.