Hi, @Nikolay Alexeev , To add a custom soap message header, you can use messageheader or messageinspector, For more information, you can refer to this link: How to add custom soap headers in wcf? Although it is a long time ago, it is still useful.
----------
If the response is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.
Best regards,
Theobald Du