Subscription error: Error: Socket closed with event 1002 RSV1 set, bad opcode 7, bad MASK at Object.error

I followed the gqlgen guide on setting up graphql in a Gin project and then tried to also add support for subscriptions.
Everything works flawlessly except for subscriptions.
When testing it out in the playground, I get the following error:

`Error: Socket closed with event 1002 RSV1 set, bad opcode 7, bad MASK at Object.error`

I am sure I am just missing something or made a mistake in my configuration, but for the life of me, cannot see where.

I created the following graphql handler which includes the AddTransport method for subscriptions:

```go
// graphql.go

func GraphqlHandler() gin.HandlerFunc {
// NewExecutableSchema and Config are in the generated.go file
// Resolver is in the resolver.go file
h := handler.NewDefaultServer(graph.NewExecutableSchema(graph.Config{Resolvers: &graph.Resolver{}}))

h.AddTransport(&transport.Websocket{}) // <== Added Subscription support

return func(c *gin.Context) {
h.ServeHTTP(c.Writer, c.Request)
}
}

// Defining the Playground handler
func PlaygroundHandler() gin.HandlerFunc {
h := playground.Handler("GraphQL", "/query")

return func(c *gin.Context) {
h.ServeHTTP(c.Writer, c.Request)
}
}
```

My routes file:
```go
// routes.go
func SetupRouter() *gin.Engine {
r := gin.Default()

// ... removed for brevity

r.Any("/query", graphql.GraphqlHandler())
r.GET("/", graphql.PlaygroundHandler())

// ... removed for brevity

return r
}
```

I would appreciate any assistance.
Many thanks!

### versions
- gqlgen version: `v0.17.45`
- go version: `go1.21.5 darwin/arm64`