generate command failing building Kotlin

[PeterJCLaw]

I'm trying out smarttype using the examples/webExample folder in this repo and I'm hitting a compiler error when running the generate command.

Output:

$ java -jar ../../../smartype-generator-1.7.0.jar generate
Extracting mParticle Data Plan
Found 16 mParticle data points.
Creating API with 16 message schema(s).
Unable to find name for schema: {"properties":{"data":{"additionalProperties":true,"properties":{},"required":[],"type":"object"},"event_type":{"const":"product_action"}}}
Unable to find name for schema: {"properties":{"data":{"additionalProperties":true,"properties":{},"required":[],"type":"object"},"event_type":{"const":"product_action"}}}
Found name: Email Sends
Found name: Email Opens
Found name: Email Deliveries
Found name: Email Bounces
Found name: Place Order
Found name: Menu
Found name: Home
Found name: Checkout
Unable to find name for schema: {"additionalProperties":false,"properties":{"$FirstName":{"description":"","type":"string"},"$Age":{"description":"","type":"number"},"$LastName":{"description":"","type":"string"},"payment":{"description":"","type":"string"},"favorite_store":{"description":"","type":"string"},"favorite_sku":{"description":"","type":"string"},"$Zip":{"description":"","type":"number"},"event_type":{"const":"user_attributes"}},"required":[]}
Unable to find name for schema: {"additionalProperties":false,"properties":{"email":{"description":"","type":"string"},"customerid":{"description":"","type":"string"},"ios_idfa":{"description":"","type":"string"},"android_aaid":{"description":"","type":"string"},"other":{"description":"","type":"string"},"ios_idfv":{"description":"","type":"string"},"device_application_stamp":{"description":"","type":"string"},"event_type":{"const":"user_identities"}},"required":[],"type":"object"}
Found name: Attribution
Found name: Choose Item
Found name: Set Pickup
Found name: Search Item

> Configure project :buildSrc
WARNING: Unsupported Kotlin plugin version.
The `embedded-kotlin` and `kotlin-dsl` plugins rely on features of Kotlin `1.9.20` that might work differently than in the requested version `1.9.22`.

> Task :buildSrc:compileKotlin FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':buildSrc:compileKotlin'.
> Inconsistent JVM-target compatibility detected for tasks 'compileJava' (17) and 'compileKotlin' (21).
  
  Consider using JVM Toolchain: https://kotl.in/gradle/jvm/toolchain
  Learn more about JVM-target validation: https://kotl.in/gradle/jvm/target-validation 

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Run with --scan to get full insights.
> Get more help at https://help.gradle.org.

Deprecated Gradle features were used in this build, making it incompatible with Gradle 9.0.

You can use '--warning-mode all' to show the individual deprecation warnings and determine if they come from your own scripts or plugins.

For more on this, please refer to https://docs.gradle.org/8.5/userguide/command_line_interface.html#sec:command_line_warnings in the Gradle documentation.

BUILD FAILED in 409ms
2 actionable tasks: 2 executed

I'm on Ubuntu 22.04 with openjdk-11-jre (via default-jre) and openjdk-21-jre installed.
Java version:

$ java --version
openjdk 21.0.4 2024-07-16
OpenJDK Runtime Environment (build 21.0.4+7-Ubuntu-1ubuntu222.04)
OpenJDK 64-Bit Server VM (build 21.0.4+7-Ubuntu-1ubuntu222.04, mixed mode, sharing)

I've tried clearing the .smarttype directory, however that doesn't change the result.

Any suggestions for how to get this working would be appreciated.