Created the project from https://start.spring.io/ and added a dependency API gateway as below

plugins {
    java
    id("org.springframework.boot") version "3.3.0"
    id("io.spring.dependency-management") version "1.1.5"
}

group = "fete.bird"
version = "0.0.1-SNAPSHOT"

java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(21)
    }
}

repositories {
    mavenCentral()
}

extra["springCloudVersion"] = "2023.0.2"

dependencies {
    implementation("org.springframework.cloud:spring-cloud-starter-gateway-mvc")
    testImplementation("org.springframework.boot:spring-boot-starter-test")
    testRuntimeOnly("org.junit.platform:junit-platform-launcher")
}

dependencyManagement {
    imports {
        mavenBom("org.springframework.cloud:spring-cloud-dependencies:${property("springCloudVersion")}")
    }
}

tasks.withType<Test> {
    useJUnitPlatform()
}

Yaml configuration

spring:
  application:
    name: api-gateway
  cloud:
    gateway:
      routes:
        - id: course-route
          uri: ${COURSE_SERVICE_URL:http://localhost:8081}
          predicates:
            - Path=/course/**
          filters:
            - AddRequestHeader=X-Tenant,acme
            - AddResponseHeader=X-Genre, fantancy

Facing the issue 404

Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.

Sat Jun 08 20:40:28 AEST 2024
There was an unexpected error (type=Not Found, status=404).