I have recently arranged a job with a client based in Sweden. I asked the client for the company’s VAT number, and he sent me a number with the format SE123456-7890. I tested the number (without the hyphen, since you should always remove hyphens and spaces when entering a VAT number) on the VIES website and was told the number was invalid. The VIES website lists the formats of VAT numbers for each EU member state, and says that Swedish numbers contain 12 digits. Mine, as you can see, only had 10.
Fortunately the Wikipedia’s list of formats gives additional information. It says that all Swedish numbers end in 01, and gives a link to a Swedish website. Although I don’t speak Swedish, I do understand enough words to see that it’s saying that you add 01 to convert a national number to an international VAT number. I tried adding 01 to the number, and sure enough the VIES website gave me the name of my client’s company, thus confirming that I had the correct number.
So, if a Swedish-based client sends you a 10-digit, rather than a 12-digit, VAT number, just add 01 to the end of it.