What am I missing? I have

{:db/ident       :simple1/position+offset
 :db/valueType   :db.type/tuple
 :db/tupleTypes  [:db.type/long :db.type/long]
 :db/cardinality :db.cardinality/many
 :db/noHistory   true}

(d/transact conn {:tx-data [{:db/id                   114349209391875
                             :simple1/position+offset [0 6]}]})

you have a cardinality many tuple

but you are inputting a single tuple

ahhh yes, that’s different, I expected it to work like in the example :man-facepalming:

so it is looking for a Seq where it sees a 0