Clicking on the IXL Learning link in Canvas can result in the message, “Error code 21: We could not sign you into IXL with Canvas at this time.”

Deleting cookies (presumably either the IXL or Canvas cookies, but I deleted all of them) will fix this problem. Note: I tried clearing the cache first, and that didn’t fix the problem, so it is possible that you need to both clear the cache and delete cookies.