Updating external list from sharepoint workflow - error

I've created page workflow to update data in external list:

When I execute this workflow, I get an error. I don't know what causes the error:

I've read about permissions to the Sharepoint system account. I feel like I've tried everything. Do you have any ideas what can cau开发者_JAVA技巧se this error ? Is there any way of debugging such workflows in Sharepoint designer ? I've tried reading Sharepoint logs, but nothing interesting there.

TIA for any clues.

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I've managed to do that, I needed to configure Secure Store Service application:

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