Extended hours rejecting everything with HTTP422

What’s the recommended format for the simplest extended hours trade: sell 1 share of asset __ at market?

Operations that perform fine during market hours seem to consistently return HTTP422 in extended hours today.


Also of note:
The “Trade __” UI at the right of https://app.alpaca.markets/paper/stocks/TSLA does not seem to work in extended hours. Perhaps add a checkbox to this web UI to allow for requesting an extended hours trade there?

In case anybody else runs into this, I think the problem is that I got confused w/r/t timezones.

Extended hours closes as 7pm ET.

Between 7pm ET and the next pre-market extended hours:

  • extended_hours=true: HTTP422 is returned
  • extended_hours=false: placing trades with some parameters are allowed (as documented), but will not be acted upon until the market open


Looks like I got it mostly right. More details under “Extended Hours Trading” @

More specifically this part triggers HTTP422:
If the order is submitted between 6:00pm and 8:00pm ET on a market day, the order request is returned with error. Alpaca reserves this time window for future expansion of supported hours.