What kind of upgrade? Did you have the page open for a long time? I wasn’t able to reproduce this.
I am on 5.6.1, looking to run the update to 5.7.5. I usually export the system before doing the update.
I go to Tools > Redirection > Import/Export. I choose Everything / JSON and immediately click on Download.
I get the message described above.
Ok, so the problem sounds like its on 5.6.1? Does it exist on the latest version?
I don’t know, because I haven’t updated, because I can’t export my Redirect information before I do so.
. . .
Okay, I went ahead and sort of manually backed it up — I did the View of the export, and copy-pasted the window’s contents into a text file. I did this with both CSV and JSON.
I ran the upgrade. It seemed to go okay.
When I went to the Redirects page, I got “API response validation failed: monitor_post: Invalid input: expected number, received string” … but the REST API tested Green/Good.
Support page all Green/Good.
Purged cache. Support page still all Green/Good.
Redirects page … no error thrown. … now okay.
And tested, and JSON Export now works without a problem. So … problem solved, I guess.