gradle-bintray-plugin Plugin [id: 'com.jfrog.bintray', version: '1.+'] was not found

I'm trying to use the gradle plugin gradle-bintray-plugin.

Currently using Gradle 4.4

Following the tutorial in the github page I should add the plugin in this way:

plugins {
    ...
    id "com.jfrog.bintray" version "1.+"
}

I'm receiving this error message and not being able to continue:

Plugin [id: 'com.jfrog.bintray', version: '1.+'] was not found in any of the following sources:

• Gradle Core Plugins (plugin is not in 'org.gradle' namespace)
• Plugin Repositories (dynamic plugin versions are not supported) Open File

Dynamic versions were maybe authorized in the past for the plugins block (as the tutorial gives it as an example) but now it's forbidden

if (versionSelectorScheme.parseSelector(markerVersion).isDynamic()) {
    result.notFound(SOURCE_NAME, "dynamic plugin versions are not supported");
    return;
}

But it's not the case for the old buildscript way and the below code is working fine with Gradle 4.10

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.jfrog.bintray.gradle:gradle-bintray-plugin:1.+'
    }
}