Passing Header from one request to another in gatling

Question

I am trying to pass a token from responseHeader of the 1st request to the conseqtive requests in a loop. However, I keep getting error stating the "continuationToken" (as in the example) is not defined

val httpProtocol = http
    .baseUrl("some-base-url")

  val scn = scenario("Scenario for 'Get store assortments by storeId'")
    .exec(http("request_1")
      .get("endpoint1")
      .header("api-key","api-key")
      .queryParam("param", true)
      .check(header("continuationToken").saveAs("${continuationToken}")))
    .doWhile(session => session("${continuationToken}").as[String] != null) {
      exec(http("request_2")
        .get("endpoint1")
        .header("api-key", "api-key")
        .queryParam("param", true)
        .queryParam("continuationToken", "${continuationToken}")
        .check(header("continuationToken").saveAs("${continuationToken}")))
    }
        setUp(scn.inject(atOnceUsers(1))).protocols(httpProtocol)

Error:

================================================================================
---- Global Information --------------------------------------------------------
> request count                                          1 (OK=0      KO=1     )
> min response time                                    129 (OK=-      KO=129   )
> max response time                                    129 (OK=-      KO=129   )
> mean response time                                   129 (OK=-      KO=129   )
> std deviation                                          0 (OK=-      KO=0     )
> response time 50th percentile                        129 (OK=-      KO=129   )
> response time 75th percentile                        129 (OK=-      KO=129   )
> response time 95th percentile                        129 (OK=-      KO=129   )
> response time 99th percentile                        129 (OK=-      KO=129   )
> mean requests/sec                                      1 (OK=-      KO=1     )
---- Response Time Distribution ------------------------------------------------
> t < 800 ms                                             0 (  0%)
> 800 ms < t < 1200 ms                                   0 (  0%)
> t > 1200 ms                                            0 (  0%)
> failed                                                 1 (100%)
---- Errors --------------------------------------------------------------------
> status.find.in([200, 209], 304), found 400                          1 (50.00%)
> request_2: Failed to build request: No attribute named 'contin      1 (50.00%)
uationToken' is defined 
================================================================================

Answer 1

.saveAs("${continuationToken}") should be .saveAs("continuationToken")

${ (deprecated syntax, now it's #{), is used in EL to refer to the session attribute, not when you're creating the session attribute. Giving it such a weird name will make it impossible to parse correctly in EL.

Answer 2

Your request_1 request fails: status.find.in([200, 209], 304), found 400. Hence, there's no way it can successfully capture the expected header: it's most likely only present when the request succeeds with 200.

Lower the logging level in the logback conf file, check your payload and then figure out why your server is responding with "400: Bad Request".