Internet Reachability Verifier helps you be sure that the internet can be truly reached. Application.internetReachability isn't enough to know that. This is first asset of its kind (check online connectivity). It's also very small: there's only a few files, you only need a single MonoBehaviour - no nonsense of hundreds of extra files! It's actively updated. It's first to support network security config added in Android 9.

Scroll all the way down to see what's new in latest version.

Also check out the Internet Reachability Verifier website.

Accompanying pdf manual contains more details of each feature listed below.
• Automatically monitors and verifies internet reachability, implemented using a light-weight coroutine.
• If internet connectivity stops working middle of your own networking and you get error codes from some networking library, you can ask for reverification of the internet reachability (this asset will not actively monitor loss of effective networking, as that would use up user's mobile data quota unnecessarily).
• 13 different captive portal detection methods: Google204, Google204HTTPS, GoogleBlank, MicrosoftNCSI, MicrosoftNCSI_IPV6, Apple, Apple2, AppleHTTPS, Ubuntu, UbuntuHTTPS, MicrosoftConnectTest, MicrosoftConnectTest_IPV6, Custom.
• Default setting is to automatically pick a suitable ("native") captive portal detection method by platform.
• Optional delegate for matching returned data for using custom method.
• Optionally append cache buster to url when using the custom method.
• Detailed internet access status property (Offline, PendingVerification, Error, Mismatch, NetVerified).
• Easy callback for listening to changes in the internet access status property (optional).

About the implementation:
• Works with Desktop, Mobile and WebGL platforms
• No native code libraries.
• C# source code included.
• Small footprint.
• Supports Unity 2020, 2019, 2018, 2017, 5, 4 and 3.5.7 (no Pro version required for older Unity versions) - v1.2.3 is last one to support the oldest legacy Unity versions.

NEW in v1.2.3:
• Fixes for Unity 2020.2+ compatibility.
• This is the last version to support legacy Unity versions from 3.5.7 to 5.6.6. (Likely support for Unity 5.6.7 will continue.)
NEW in v1.2.2:
• Verified support for Enter Play Mode without Domain/Scene Reload
• Removed GUILayer components
NEW in v1.2.1:
• Lowered Android minimum sdk version requirement.
NEW in v1.2.0:
• WebGL and Facebook platform support.
• Support for Android 9 security config, where cleartext http traffic is disabled by default (similar to iOS ATS).
• Compatibility verified up to Unity 2018.3.
• New detection methods: Google204HTTPS, UbuntuHTTPS, MicrosoftConnectTest, MicrosoftNCSI_IPV6, MicrosoftConnectTest_IPV6 (the IPV6 ones can verify if the network is IPV6-capable!).
• UnityWebRequest is now used with Unity 2018.3+

Internet Reachability Verifier Website | Forum Thread

Also from Strobotnik:
• Klattersynth TTS (NEW!)
• Google Universal Analytics for Unity
• Dynamic Text