X-Stape-User-Id as external_id facebook conversion API

I want this to use X-Step-User-Id as external id facebook conversion Api, is that the correct data?
Then I tried to apply it to my GTM, there was no request header variable like the instructions here >>

I really appreciate everyone who wants to explain and help

Can you provide a screenshot of what you have in the request headers?
Have you activated power up on this container?

I’ve enabled the container settings for x-stape-user-id

The question is, how do I create variables in my GTM web container? I tried looking for instructions and they mentioned creating an HTTP Header variable, but I don’t see that option in my web container variables

Sorry, I’m a beginner about this gtm server.

It can’t technically be sent to you on a web container from the Stape side.
But you can configure the transfer of this from the server container to the web container, here I have described in general how it can be configured: X Stape User ID as External ID Facebook CAPI.