I get the same error. The program has not changed since 2018, so I think it has to do with the online database, even though it seems to still exist and look fine. I thought maybe someone created an account with a weird name (like a special character) that broke something, but it didn't work either after resetting the whole login table.
I would need more time to investigate. I haven't touched this program since 2018 and I am not familiar with Python anymore.
How badly do you want to use Konjugaattori? :D