Editing copy rules while the copier runs
Your copy rules live on the Trade Desk, under Manage rules. While the copier runs they are read-only: every rule field is greyed, and a banner above the tabs explains why: "Copying is running. Follow and Close stay live; the greyed settings unlock when you stop." Click a greyed field and it says so again: "Stop copying to change these settings." The API refuses the same way, with a 409: "The copier is running: stop it before changing your copy rules."
Why the lock exists
The engine reads your configuration once, when it starts. An edit made mid-run would either do nothing until the next restart (silently) or, worse, re-target accounts that already hold positions under the old rules. Neither is acceptable, so the honest answer is to refuse. Stop, edit, save, start again.
Locked settings include the leader account and instrument, follower sizing, Max, Cross order, adding an account to a group, adding, renaming or deleting groups. The "Blocked instruments" list, on Settings, Copier, is locked the same way.
What still works live
Two things are deliberately allowed while the copier runs, because they change which rules are on, never the rules themselves:
- The Follow switch, per account and per group, on the Trade Desk. Flip it off and that account stops copying this group's leader; its settings are remembered. Flip it back on and it copies again, in this group only. The box on a login's header row (Sort by Connection) does the same for that login's accounts at once. Two things stay greyed until you stop: an account the group does not hold yet ("Stop copying to add an account to this group."), and an account that was switched off in every group when copying started: "[account] was switched off in every group when copying started. Stop copying, switch it on, then start again."
- Pause all / Resume all, also on the Trade Desk, on the right of the tab row while copying runs (on a phone, under the Sort row). The same switch, applied to everyone at once. When every follower is paused it reads Resume all, and then it shows even while the copier is stopped, so you never have to start copying with everyone off just to switch them back on.
Renaming a group is cosmetic, but its rename pencil only shows while the copier is stopped, so rename it once you have stopped.
Anything structural sent to the Follow-switch endpoint is refused outright: "These changes go beyond turning copying on or off for an account. Make them on the Trade Desk, under Manage rules."
Reading your rules is never locked. Press Manage rules on the Trade Desk at any time, running or stopped: each group's tab shows its leader, every account with its sizing, Cross order and Max. The "Blocked instruments" list is on Settings, Copier. While copying runs they are greyed; stop the copier and the same fields become editable in place, with nothing to open or close.
Quick answers
Why does my save return 409?
The copier started while you were editing. Your changes are kept, and the amber save bar under the rules says: "Copying started, so these changes cannot be saved now. Stop copying to save them, or discard them." Stop it from the top bar (on a phone, the dock on the Desk tab), press Save changes, then start again.
Can I pause one follower without stopping everything?
Yes. The Follow switch on the Trade Desk works mid-session. It switches the account off in that group only, in place; sizing and settings survive, and the row's Status reads Paused (and Off once the copier is stopped).
Does stopping the copier close my positions?
Stopping halts copying; it is not a close. If you want positions closed as well, that is what Flatten all is for. See engine controls explained.