How do I replace an absolute path in XQUERY?

Question

I'm trying to replace the current query, which retrieves a logo from my IDM database, with a new query that uses the customer number from my XML instead.

Current query:

{
   "xpath": null,
   "hide": null,
   "image": {
        "xqueries": [
          "/ZZ_Etailer_Logo[@Customer=\"GREE73\"]"
        ]
      }
    }

New query:

    {
      "xpath": null,
      "hide": null,
      "image": {
        "xqueries": [
          "/ZZ_Et
ailer_Logo[@Customer=\"{/M3OutDocument/DataArea/Document/DocumentHeader/OQCONA}\"]"
     ]
   }
}

I was hoping that using OQCONA (customer number) would retrieve the correct logo, but it's not returning anything. What am I doing wrong?

The original query works, but it only retrieves one logo, which is not suitable. I don't want to create multiple documents to solve this issue.