We have a printer at our office, namely a Samsung CLX-6260ND. About 2 months ago it was reported that scan to email no longer works. After checking the smtp settings, sure enough, I found that the smtp address somehow magically disappeared. The admin user is not known to anyone but me and another IT admin, and we did not remove the smtp address. So I assumed it was a random thing that just happened and added the address back. When looking at other details in the SyncThru portal, I noticed that the firmware version is pretty old, so I upgraded it. https://support.hp.com/us-en/drivers/closure/samsung-clx-6260-color-laser-multifunction-printer-series/16462350 The upgrade went really smoothly, the only thing was we could not print in color with our existing windows drivers, so I had to install a fresher one, then there were no problems. So basically at this stage everything was fine, scan to email worked, color printing worked, address book I believe was also populated.
A few weeks went by and our HR once again reporting problems with the printer. According to them, the firmware upgrade wiped out the address book (#doubt) and they are no longer able to add to it as it throws an error.
This is where my current problem is, we cannot add entries to the address book, it comes back with the same error every time. I tried different browsers, even tried to send the POST request from insomnia, I am getting the same error.

Some Errors were reported.Your request failed. Please try again
It comes from a POST to http:///sws/app/addressbook/GetUsedSpeedNoInABook.jsp
And the response:

I tried to look for this error number but could not find anything. https://www.manua.ls/samsung/clx-6260nd/manual?p=352
I made an export from our active directory and saved the addresses as csv, made it fit the schema I got by exporting the (empty) address book. When I try to import the csv, I get the following:
The 2 responses from this are:
{success:true, TotalCount: 1, ImportedCount: 0} {success: true, TotalCount: 0, start: 0, limit: 0, recordData: [ ]}
So I got stuck here as well... Then as a last resort I set up LDAP and try to import users like that, it also fails.
(details are of course blanked out)
And guess what I am getting as I press Import: Some Errors were reported.Your request failed. Please try again
I tried to restart/power cycle the printer countless times, did a full network reset, played with nearly all the checkboxes/settings, reinstalled the firmware a few times, all with no positive result. Please if anyone has any suggestion how to troubleshoot this further, let me know. Thanks!