I'm really glad to see that you're working on Jenkins plugin, it is essential part of our testing framework.
It seems like the "File URL"(probably should be named Test Results Location, it's not a URL) field doesn't accept relative paths.
When running a build on an jenkins linux agent hwile the master Jenkins runs on windows, the plugin can't find results file see stack trace below.
INFO: Retrying request to {s}->https:java.io.FileNotFoundException: \opt\jenkins\jenkins-stg-slave\workspace\POC\SCM-JIRATest\target\surefire-reports\TEST-somepackage.xml (The system cannot find the path specified)
at java.io.FileInputStream.open0(Native Method)
at java.io.FileInputStream.open(FileInputStream.java:195)
at java.io.FileInputStream.<init>(FileInputStream.java:138)
at org.apache.http.entity.mime.content.FileBody.writeTo(FileBody.java:116)
at org.apache.http.entity.mime.AbstractMultipartForm.doWriteTo(AbstractMultipartForm.java:134)
at org.apache.http.entity.mime.AbstractMultipartForm.writeTo(AbstractMultipartForm.java:157)
at org.apache.http.entity.mime.MultipartFormEntity.writeTo(MultipartFormEntity.java:113)
at org.apache.http.impl.DefaultBHttpClientConnection.sendRequestEntity(DefaultBHttpClientConnection.java:158)
at org.apache.http.impl.conn.CPoolProxy.sendRequestEntity(CPoolProxy.java:162)
at org.apache.http.protocol.HttpRequestExecutor.doSendRequest(HttpRequestExecutor.java:237)
at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:122)
at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:271)
at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:184)
at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:88)
at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:184)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:82)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:107)
at com.qmetry.UploadToServer.uploadToTheServer(UploadToServer.java:126)
at com.qmetry.TestReportDeployPublisher.perform(TestReportDeployPublisher.java:528)
at hudson.tasks.BuildStepCompatibilityLayer.perform(BuildStepCompatibilityLayer.java:81)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:744)
at hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:690)
at hudson.model.Build$BuildExecution.post2(Build.java:186)
at hudson.model.AbstractBuild$AbstractBuildExecution.post(AbstractBuild.java:635)
at hudson.model.Run.execute(Run.java:1749)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
at hudson.model.ResourceController.execute(ResourceController.java:97)
at hudson.model.Executor.run(Executor.java:421)