First, configure the plugin by specifying your certificates. You also need to register to Swish to use the Sandbox environment (https://developer.swish.nu/documentation/environments#user-enrolment)
Use API calls to create/check payment requests / refunds / payouts.


Please observer payouts need a signing procedure as described here:  https://developer.swish.nu/documentation/guides/make-a-payout

It basically involves creating an md5 hash or the payload and then signing it using RSA (SHA521) with the test signing certificate provided by Swish (see above).

Haven't done this in Bubble yet, only in Java as per Swish instructions, but apparently these plugins could be used to generate the hash and maybe the RSA signature:


HASH

https://bubble.io/plugin/cryptographic-hashes-1654419731259x909591253244969000

RSA

https://bubble.io/plugin/rsa-sha256-hash-backend-1600934426535x594017963721097200

Or you could use a trustable service online with an API to do this.

You can manually create the hash and signature using these online services:


HASH:
https://emn178.github.io/online-tools/sha512.html

SIGNATURE:
https://www.lddgo.net/en/encrypt/rsa-sign-verify#toolNoteIframe

NOTE: The payload must be exactly the same when being sent to Swish in the request and when you are calculating the HASH! This includes spaces/carriage line and UTF-8.