Expect 204 found 400 in REST API - rest-assured

Question

Please suggest possible solution for the below Rest API code.
I just tried to assign the created issue to one person in JIRA.
There is another piece of code where I have created one issue. That works without any issue but this is not working.
Here is the code below:
....................................................................................................................................................................................................................................................................................................................................................................................................................................
public class JIRA_Update {
Properties prop=new Properties();
#BeforeTest
public void getData() throws IOException
{
FileInputStream fis= new FileInputStream(System.getProperty("user.dir")+"\\src\\files\\environment.properties");
prop.load(fis);
}
#Test
public void assignJIRA()
{
RestAssured.baseURI=prop.getProperty("HOST2");
given().header("content-type","application/json").
header("Cookie","JSESSIONID="+reusableMethods.getSessionID()).
body("{" +
"\"name\":\"Ansuman\"" +
"}").
when().
put("/rest/api/2/issue/10004/assignee").
then().statusCode(204);
}
Below error I got:
[RemoteTestNG] detected TestNG version 6.7.0
[TestNG] Running:
C:\Users\AnsumanPrasad\AppData\Local\Temp\testng-eclipse-1620457977\testng-customsuite.xml
Request method: PUT
Request URI: http://localhost:8080/rest/api/2/issue/10100/assignee
Proxy: <none>
Request params: <none>
Query params: <none>
Form params: <none>
Path params: <none>
Headers: Cookie=JSESSIONID=D7A94750CC1AC453FB60054EFCC0340B
Accept=*/*
Content-Type=application/json; charset=UTF-8
Cookies: <none>
Multiparts: <none>
Body:
{
"name": "Ansuman"
}
Request method: PUT
Request URI: http://localhost:8080/rest/api/2/issue/10100/assignee
Proxy: <none>
Request params: <none>
Query params: <none>
Form params: <none>
Path params: <none>
Headers: Cookie=JSESSIONID=D7A94750CC1AC453FB60054EFCC0340B
Accept=*/*
Content-Type=application/json; charset=UTF-8
Cookies: <none>
Multiparts: <none>
Body:
{
"name": "Ansuman"
}
HTTP/1.1 400
X-AREQUESTID: 1130x39x1
X-ASESSIONID: 8tbrup
X-XSS-Protection: 1; mode=block
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
Content-Security-Policy: frame-ancestors 'self'
X-ASEN: SEN-L15668709
X-Seraph-LoginReason: OK
Set-Cookie: atlassian.xsrf.token=B1FY-RQO1-RBZ3-U5XU_bcbf0b7117c072a927e06729133c3b7fa914b65b_lin; Path=/
X-AUSERNAME: admin
Cache-Control: no-cache, no-store, no-transform
Content-Encoding: gzip
Vary: User-Agent
Content-Type: application/json;charset=UTF-8
Transfer-Encoding: chunked
Date: Thu, 02 Jul 2020 13:21:12 GMT
Connection: close
{
"errorMessages": [
],
"errors": {
"assignee": "User 'Ansuman' does not exist."
}
}
FAILED: assignJIRA
java.lang.AssertionError: 1 expectation failed.
Expected status code <204> but was <400>.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at org.codehaus.groovy.reflection.CachedConstructor.invoke(CachedConstructor.java:72)
at org.codehaus.groovy.reflection.CachedConstructor.doConstructorInvoke(CachedConstructor.java:59)
at org.codehaus.groovy.runtime.callsite.ConstructorSite$ConstructorSiteNoUnwrap.callConstructor(ConstructorSite.java:84)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallConstructor(CallSiteArray.java:59)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callConstructor(AbstractCallSite.java:263)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callConstructor(AbstractCallSite.java:277)
at io.restassured.internal.ResponseSpecificationImpl$HamcrestAssertionClosure.validate(ResponseSpecificationImpl.groovy:493)
at io.restassured.internal.ResponseSpecificationImpl$HamcrestAssertionClosure$validate$1.call(Unknown Source)
at io.restassured.internal.ResponseSpecificationImpl.validateResponseIfRequired(ResponseSpecificationImpl.groovy:674)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.codehaus.groovy.runtime.callsite.PlainObjectMetaMethodSite.doInvoke(PlainObjectMetaMethodSite.java:43)
at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite$PogoCachedMethodSiteNoUnwrapNoCoerce.invoke(PogoMetaMethodSite.java:193)
at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite.callCurrent(PogoMetaMethodSite.java:61)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:185)
at io.restassured.internal.ResponseSpecificationImpl.statusCode(ResponseSpecificationImpl.groovy:126)
at io.restassured.specification.ResponseSpecification$statusCode$0.callCurrent(Unknown Source)
at io.restassured.internal.ResponseSpecificationImpl.statusCode(ResponseSpecificationImpl.groovy:134)
at io.restassured.internal.ValidatableResponseOptionsImpl.statusCode(ValidatableResponseOptionsImpl.java:89)
at io.restassured.internal.ValidatableResponseImpl.super$2$statusCode(ValidatableResponseImpl.groovy)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:107)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:323)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1262)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuperN(ScriptBytecodeAdapter.java:144)
at io.restassured.internal.ValidatableResponseImpl.statusCode(ValidatableResponseImpl.groovy:142)
at io.restassured.internal.ValidatableResponseImpl.statusCode(ValidatableResponseImpl.groovy)
at Demo.JIRA_Update.assignJIRA(JIRA_Update.java:58)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:80)
at org.testng.internal.Invoker.invokeMethod(Invoker.java:715)
at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:907)
at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1237)
at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:127)
at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:111)
at org.testng.TestRunner.privateRun(TestRunner.java:767)
at org.testng.TestRunner.run(TestRunner.java:617)
at org.testng.SuiteRunner.runTest(SuiteRunner.java:334)
at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:329)
at org.testng.SuiteRunner.privateRun(SuiteRunner.java:291)
at org.testng.SuiteRunner.run(SuiteRunner.java:240)
at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:51)
at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:85)
at org.testng.TestNG.runSuitesSequentially(TestNG.java:1197)
at org.testng.TestNG.runSuitesLocally(TestNG.java:1122)
at org.testng.TestNG.run(TestNG.java:1030)
at org.testng.remote.AbstractRemoteTestNG.run(AbstractRemoteTestNG.java:115)
at org.testng.remote.RemoteTestNG.initAndRun(RemoteTestNG.java:251)
at org.testng.remote.RemoteTestNG.main(RemoteTestNG.java:77)
===============================================
Default test
Tests run: 1, Failures: 1, Skips: 0
===============================================
===============================================
Default suite
Total tests run: 1, Failures: 1, Skips: 0
===============================================
[TestNG] Time taken by org.testng.reporters.XMLReporter#52af6cff: 96 ms
[TestNG] Time taken by org.testng.reporters.EmailableReporter#9f70c54: 13 ms
[TestNG] Time taken by org.testng.reporters.JUnitReportReporter#50f8360d: 11 ms
[TestNG] Time taken by org.testng.reporters.SuiteHTMLReporter#6615435c: 87 ms
[TestNG] Time taken by org.testng.reporters.jq.Main#617c74e5: 156 ms
[TestNG] Time taken by [TestListenerAdapter] Passed:0 Failed:0 Skipped:0]: 23 ms