Getting "operation is not allowed when the object is closed" error on insert but not on select

[MagicMustache]

Hello,
I'm getting the error "operation is not allowed when the object is closed" when trying to insert into a table, but in the same function i'm doing a select that works fine.
Here is my insert query :
await connection.query("insert into Variants (CatalogCode,Variant,MeleePrice,StonePrice,RingPrice,PrRing,PrMelee,PrStone) values ('"+variantsToAdd[i].CatalogCode+"','"+variantsToAdd[i].Variant+"',"+variantsToAdd[i].MeleePrice+"," +variantsToAdd[i].StonePrice+","+variantsToAdd[i].RingPrice+","+variantsToAdd[i].PrRing+","+variantsToAdd[i].PrMelee+","+variantsToAdd[i].PrStone+")")