Tax on one-time contract for foreign company
I'm resident and working in Sweden with a regular salaried job here. On the side of that last year I had one small time-limited extra job that I did (working from home) for an international company based in the UK. I received a one-time payment based on the amount of work done with no deductions etc. The payment was more than 10000 SEK but not very much more. From the point of view of the international company I am an independent contractor and they don't undertake to do any extra paperwork beyond the contract and payment.
My question is what is the simplest correct way to declare this income and pay the appropriate tax? I am hoping that I don't need to go through a lot of paperwork to set up my own company for this comparatively small amount. I would do such a one-off job again in the future but no more than once a year.
Thanks in advance. (Det går bra att svara på svenska förresten.)