why doesn't the gradle repository definition work?

I'm at a loss why gradle is ignoring the 'repository' section of a pretty simple build.gradle file. We're behind a firewall, using a JFrog repository to use our own scanned versions of things, not Maven central. When I run 'gradle compile', I get:

FAILURE: Build failed with an exception.

• Where: Build file '/Users/exampleuser/src/example/tlp-platform-portal/build.gradle' line: 2

• What went wrong: Plugin [id: 'org.springframework.boot', version: '2.6.3'] was not found in any of the following sources:

• Gradle Core Plugins (plugin is not in 'org.gradle' namespace)
• Plugin Repositories (could not resolve plugin artifact 'org.springframework.boot:org.springframework.boot.gradle.plugin:2.6.3') Searched in the following repositories: Gradle Central Plugin Repository

But my build.gradle has no mention of Gradle central; the file looks like the attached...

suggestions, 'RTFM's etc welcomed...

thank you in advance Chris

--------build.gradle---------------------

    id 'org.springframework.boot' version '2.6.3'
    id 'io.spring.dependency-management' version '1.0.11.RELEASE'
    id 'java'
    id 'war'
}

group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'

repositories {
    maven {
        url 'https://example.jfrog.io/artifactory/penalty-maven-local'
        credentials {
            username = System.getenv('ARTIFACT_USERNAME')
            password = System.getenv('ARTIFACT_PASSWORD')
        }
    }
    maven {
        url 'https://example.jfrog.io/artifactory/dha-gradle-plugin-remote-cache'
        credentials {
            username = System.getenv('ARTIFACT_USERNAME')
            password = System.getenv('ARTIFACT_PASSWORD')
        }
    }
    maven {
            url 'https://example.jfrog.io/artifactory/plugins-release'
            credentials {
                    username =System.getenv('ARTIFACT_USERNAME')
                    password =System.getenv('ARTIFACT_PASSWORD')
            }
    }
    maven {
        url "https://example.jfrog.io/example/libs-snapshot"
        credentials {
            username = System.getenv('ARTIFACT_USERNAME')
            password = System.getenv('ARTIFACT_PASSWORD')
        }
    }
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-data-jdbc'
    implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
    implementation 'org.springframework.boot:spring-boot-starter-security'
    implementation 'org.springframework.boot:spring-boot-starter-web'
(lots more)