[SOLVED] OpenTelemetry Dynatrace: SEVERE: Failed to export spans. The request could not be executed. Full error message: Canceled

I have the following simple code:

package com.example;

import io.opentelemetry.api.OpenTelemetry;
import io.opentelemetry.api.trace.Span;
import io.opentelemetry.api.trace.Tracer;
import io.opentelemetry.context.Scope;
import io.opentelemetry.exporter.logging.LoggingSpanExporter;
import io.opentelemetry.exporter.otlp.trace.OtlpGrpcSpanExporter;
import io.opentelemetry.sdk.OpenTelemetrySdk;
import io.opentelemetry.sdk.trace.SdkTracerProvider;
import io.opentelemetry.sdk.trace.export.BatchSpanProcessor;
import io.opentelemetry.sdk.trace.export.SimpleSpanProcessor;

public class ManualOpenTelemetryExample {

    public static void main(String[] args) {
        // Step 1: Set up the OTLP exporter to send data to Dynatrace
        OtlpGrpcSpanExporter otlpExporter = OtlpGrpcSpanExporter.builder()
                .setEndpoint("<YOUR_DYNATRACE_ENDPOINT>") // Replace with your Dynatrace endpoint
                .addHeader("Authorization", "Api-Token <YOUR_API_TOKEN>") // Replace with your Dynatrace API token
                .build();

        // Step 2: Set up the LoggingSpanExporter for debugging
        LoggingSpanExporter loggingExporter = LoggingSpanExporter.create();

        // Step 3: Set up the BatchSpanProcessor with the OTLP exporter
        BatchSpanProcessor spanProcessor = BatchSpanProcessor.builder(otlpExporter).build();

        // Step 4: Set up the TracerProvider with both processors
        SdkTracerProvider tracerProvider = SdkTracerProvider.builder()
                .addSpanProcessor(spanProcessor)
                .addSpanProcessor(SimpleSpanProcessor.create(loggingExporter)) // Add logging exporter
                .build();

        // Step 5: Initialize OpenTelemetry with the TracerProvider
        OpenTelemetrySdk openTelemetry = OpenTelemetrySdk.builder()
                .setTracerProvider(tracerProvider)
                .build();

        // Step 6: Get a Tracer
        Tracer tracer = openTelemetry.getTracer("manual-instrumentation-example", "1.0.0");

        // Step 7: Simulate a workflow with multiple spans
        simulateWork(tracer);

        // Step 8: Shutdown the tracer provider to flush spans
        tracerProvider.shutdown();
    }

    /**
     * Simulates a workflow with multiple spans.
     */
    private static void simulateWork(Tracer tracer) {
        // Create a parent span for the entire workflow
        Span parentSpan = tracer.spanBuilder("workflow-operation").startSpan();
        try (Scope parentScope = parentSpan.makeCurrent()) {
            // Add attributes to the parent span
            parentSpan.setAttribute("service.name", "my-java-service");
            parentSpan.setAttribute("environment", "production");

            // Simulate step 1: Fetch data
            simulateStep(tracer, "fetch-data", 200);

            // Simulate step 2: Process data
            simulateStep(tracer, "process-data", 300);

            // Simulate step 3: Save data
            simulateStep(tracer, "save-data", 100);

            // Simulate step 4: Send notification
            simulateStep(tracer, "send-notification", 150);

        } finally {
            // End the parent span
            parentSpan.end();
        }
    }

    /**
     * Simulates a single step in the workflow.
     *
     * @param tracer       The OpenTelemetry tracer.
     * @param stepName     The name of the step.
     * @param durationMs   The duration of the step in milliseconds.
     */
    private static void simulateStep(Tracer tracer, String stepName, long durationMs) {
        // Create a span for the step
        Span stepSpan = tracer.spanBuilder(stepName).startSpan();
        try (Scope stepScope = stepSpan.makeCurrent()) {
            // Add attributes to the step span
            stepSpan.setAttribute("step.name", stepName);
            stepSpan.setAttribute("step.duration.ms", durationMs);

            // Simulate work by sleeping
            System.out.println("Executing step: " + stepName);
            Thread.sleep(durationMs);

        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            // End the step span
            stepSpan.end();
        }
    }
}

All I want to do is to create one simple java process just to test creating ingest span into Dynatrace. But I'm always ended with the following error:

$ mvn exec:java -Dexec.mainClass="com.example.ManualOpenTelemetryExample"
[INFO] Scanning for projects...
[INFO]
[INFO] --------------< com.example:manual-opentelemetry-example >--------------
[INFO] Building manual-opentelemetry-example 1.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- exec:3.5.0:java (default-cli) @ manual-opentelemetry-example ---
Executing step: fetch-data
Feb 03, 2025 3:11:25 PM io.opentelemetry.exporter.logging.LoggingSpanExporter export
INFO: 'fetch-data' : b6176f27f93041eda5e3ea2c20e27870 7942d9ee73773df1 INTERNAL [tracer: manual-instrumentation-example:1.0.0] AttributesMap{data={step.duration.ms=200, step.name=fetch-data}, capacity=128, totalAddedValues=2}
Executing step: process-data
Feb 03, 2025 3:11:25 PM io.opentelemetry.exporter.logging.LoggingSpanExporter export
INFO: 'process-data' : b6176f27f93041eda5e3ea2c20e27870 d3b9bc007fb9e028 INTERNAL [tracer: manual-instrumentation-example:1.0.0] AttributesMap{data={step.duration.ms=300, step.name=process-data}, capacity=128, totalAddedValues=2}
Executing step: save-data
Feb 03, 2025 3:11:26 PM io.opentelemetry.exporter.logging.LoggingSpanExporter export
INFO: 'save-data' : b6176f27f93041eda5e3ea2c20e27870 778ede14f1ca0d99 INTERNAL [tracer: manual-instrumentation-example:1.0.0] AttributesMap{data={step.duration.ms=100, step.name=save-data}, capacity=128, totalAddedValues=2}
Executing step: send-notification
Feb 03, 2025 3:11:26 PM io.opentelemetry.exporter.logging.LoggingSpanExporter export
INFO: 'send-notification' : b6176f27f93041eda5e3ea2c20e27870 17ce27eecaee9ac4 INTERNAL [tracer: manual-instrumentation-example:1.0.0] AttributesMap{data={step.duration.ms=150, step.name=send-notification}, capacity=128, totalAddedValues=2}
Feb 03, 2025 3:11:26 PM io.opentelemetry.exporter.logging.LoggingSpanExporter export
INFO: 'workflow-operation' : b6176f27f93041eda5e3ea2c20e27870 e350cdb78679c4e7 INTERNAL [tracer: manual-instrumentation-example:1.0.0] AttributesMap{data={environment=production, service.name=my-java-service}, capacity=128, totalAddedValues=2}
Feb 03, 2025 3:11:26 PM io.opentelemetry.sdk.internal.ThrottlingLogger doLog
SEVERE: Failed to export spans. The request could not be executed. Full error message: Canceled
[WARNING] thread Thread[#55,Okio Watchdog,5,com.example.ManualOpenTelemetryExample] was interrupted but is still alive after waiting at least 14980msecs
[WARNING] thread Thread[#55,Okio Watchdog,5,com.example.ManualOpenTelemetryExample] will linger despite being asked to die via interruption
[WARNING] NOTE: 1 thread(s) did not finish despite being asked to via interruption. This is not a problem with exec:java, it is a problem with the running code. Although not serious, it should be remedied.
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  16.700 s
[INFO] Finished at: 2025-02-03T15:11:41+08:00
[INFO] ------------------------------------------------------------------------

What could be wrong here? Is there anything missing from my code?

The idea is to test my Dynatrace instance that opentelemetry is proven to be working using Java