As far as I can see in the Ads UI, accelerated delivery (i.e. standard_delivery = false) is not compatible with automatically_select_bid = true, so maybe that’s why your campaign is uneditable in the Ads UI. Try the same call without specifying standard_delivery and let us know if the problem persists or not.
Also, the line item’s total_budget_amount_local_micro is strictly lower than the campaign’s total_budget_amount_local_micro and I think that’s why Twitter assumes you intend to create another line item in the same campaign, since you’re not attributing the full campaign budget only to this line item. Try to leave the line item’s total_budget_amount_local_micro out and see if it solves the problem.