Tradovate session conflicts: one API session per login
You press Test on a Tradovate connection and it fails with "copier is running on this Tradovate login: stop it before probing (Tradovate allows one API session per login)". Or your copier session drops around the time you signed into Tradovate's own platform. Both are the same rule surfacing.
Why it happens
Tradovate permits one API session per login. A connection test is its own session, so testing a login the running copier is already using would knock the copier off mid-session. MirrorFill refuses the test instead and tells you why. That beats silently dropping a live copy session.
Being signed into the Tradovate web or desktop platform on the same login can conflict the same way. If the copier disconnects when you open Tradovate in a browser, this is the likely cause. Auto-reconnect recovers the session, but that is downtime you didn't need.
Rithmic has the same one-session rule with a harder landing: there, a takeover stops the copier outright instead of reconnecting. See Rithmic session conflicts.
The same rule holds between MirrorFill accounts. Every account runs its own copier, and one login can drive only one of them at a time. If Test answers "This login is in use by a running copier, so it cannot be tested right now.", or Start copying says the broker login on a connection "is already in use by a running copier", a copier under a different MirrorFill account holds that login right now. Stop that copier first, or give each account its own login.
What to do
- Stop the copier before testing. Press Stop on the engine strip, run Test, then Start copying again. Testing a login the copier isn't using needs no stop. On a phone, press Stop on the Desk tab first: the Accounts tab has no engine strip.
- Give the copier its own login where you can. If you have a second Tradovate login, keep the copier on one and your own screen time on the other. They stop competing for the same session.
- Don't hammer Test. Tradovate penalizes repeated access-token requests. MirrorFill contacts each environment at most once per test, but a retry loop from your side still adds up, and after ten tests in a minute the app asks you to wait ("Too many attempts. Please wait and try again."). If a test fails, read the error and fix the cause. Don't press the button five more times.
Quick answers
Why does MirrorFill block the test instead of just running it?
Because the test would take over the login's one session and drop the running copier. A refused test is recoverable; a dropped copy session mid-trade is worse.
Can I watch my Tradovate account in the browser while copying?
On the same login it can conflict with the copier's session. Use a separate login if you have one, or accept that the copier may reconnect when you sign in.
The test failed once. Should I retry right away?
Read the error first. Repeated access-token requests are penalized by Tradovate, so a retry loop makes a bad situation worse.