Thank you for the prompt reply! The 2 second or even longer (like 30) doesn’t solve the issue. When it gets up to 60 second apart, yes it solves the issue but the wait is too long for adding 20 items etc.
The solution I eventually use is to create a recursive API call so the next thing to add to the list always comes after the previous action was done.
I luckily found how to do this by going through the link you provide. Thanks a lot!
In summary, I would recommend anyone experiencing this issue set up a recursive workflow and it will be done in seconds.