We are happy to assist with your requirement. please drop us an email with your contact details to to "nipuna at oganro dot com". we will get back to you with steps how you can integrate Swish.
Can I ask which country you're based in? The reason I ask is because the available payment gateways for each country Shopify is partnered with is different. Once I know which country you're in, I can see if Swish is partnered with Shopify for the location.
I know Swish is a Swedish payment gateway but it isn't partnered with Shopify as a gateway for Sweden.
Because Swish isn't a partnered gateway with Shopify in Sweden, it's not as simple as just adding it as your gateway in the admin. The best way for this would be to work with a Shopify Expert to add the gateway for you as some custom work. You can see the Shopify Expert directory here.
Something to note is that this is something which our development team is aware of and a feature request has been created for it. I've added your feedback to it also. Hopefully it can become available soon!
Dear @colibri21 ,
We are happy to assist you integrating Swish with you Shopify as a custom integration. Feel free to DM us, if you wish to proceed.