For Steven to recognize whether a swish payment has been successfully completed or failed, the swish sender must close the swish pop-up window that is shown when the transaction is complete by clicking the cross in the lower right corner. If the sender forgets to close the pop-up before leaving the swish app, the transaction will not be registered automatically in Steven.
However, you can easily fix this manually. Simply ask your friend to check that they've received the payment and, if so, confirm the payment under the payments tab in Steven. The debt will then be altered to an even status in the app.