What do you mean? "The laws on prostitution in Sweden make it illegal to buy sexual services, but not to sell them. Pimping, procuring and operating a brothel are also illegal. The criminalisation of the purchase, but not selling, of sex was unique when first enacted in 1999, but since then Norway and Iceland have adopted similar legislation, both in 2009." https://en.wikipedia.org/wiki/Prostitution_in_Sweden

If you make either side of a transaction illegal, the transaction is illegal, and both sides are driven underground.

There are important distinctions in the resulting power dynamics which mean that the distinctions between prohibiting both sides, prohibiting just the purchasing side, and prohibiting just the selling side significant distinctions. But all of them prohibit the exchange and force the exchange underground; you can't do that to only one side of the exchange.