The issue appears to have been resolved. The POST data is sent with two keys: fkey and closeReasonId.
I'm attempting to review an item in the Code Review SE reopen queue. After opting to leave the post closed, I select a reason and then click the button labeled Keep Closed an error notification is displayed at the top of the screen. In the console, I see the request received a 418 response. Can the response be a 2xx response soon, please?
This is occurring in Win10 & Mac OS 11.6 FF 93.0 64-bit, as well as Brave Version 1.22.71 Chromium: 89.0.4389.114 (Official Build) (x86_64), plus Safari 15.0 (166184.108.40.206.4, 16612), Chrome on iOS (with wifi disabled), MS Edge 94.0.992.50 (Official build) (64-bit) and Opera 80.0.4170.40 (x86_64).
It also happens in the Stack Overflow reopen queue.
After inspecting the POST request, it appears no POST data is getting submitted when opting to leave a question closed. When opting to reopen a question, the POST data contains 5 fields: taskTypeId, taskResultTypeId, fkey, postCommentId, and taskResultSubtypeFlags.