Deleting and then reinstalling plugin keeps same API details

Hi

So im trying to troubleshoot a problem with adding API keys. For some reason i get the 401 unauthorized error for European Production keys, even though i have triple checked they are correct and as far as i am aware the API and the merchant account is configured to use Klarna checkout (although waiting on support to get back to me to be sure) the Merchant id is K1026682.

But the main problem i am having is when i delete the plugin from WordPress then reinstall the plugin, all the previously entered API details, settings etc are still there? I wanted to delete the plugin, to remove all those settings and API details to try and enter them again on a fresh install of the plugin. Also are the API credentials stored in a file or database row anywhere? Im suspicious that maybe some old API keys are being saved and the new ones aren’t being saved correctly.

Could be a problem with the Klarna account its self as this was setup by a client, so im just trying to figure out if there is anything im doing wrong or if its the Klarna account.

Thanks