Unable to read Http request using Swagger

I created the Swagger API Definition file using the Swagger API-codegen. However, I am getting an error when I try to pass the request. Can someone plz tell me where am I making mistake? and how can I read the data?

package main

import (
	"flag"
	"fmt"
	"os"

	api "newform-api/inputform"

	"github.com/deepmap/oapi-codegen/pkg/middleware"
	"github.com/labstack/echo/v4"
	echomiddleware "github.com/labstack/echo/v4/middleware"
)

// ServerInterface represents all server handlers.
type ServerInterface interface {
	Externalhealthcheck(ctx echo.Context) error
	NewFormEntry(ctx echo.Context) error
}

func main() {
	var port = flag.Int("port", 8080, "Port for test HTTP server")
	flag.Parse()

	swagger, err := api.GetSwagger()
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error loading swagger spec\n: %s", err)
		os.Exit(1)
	}

	swagger.Servers = nil

	apiData := api.ServerInterfaceWrapper{}

	e := echo.New()
	e.Use(echomiddleware.Logger())

	e.Use(middleware.OapiRequestValidator(swagger))

	api.RegisterHandlers(e, apiData.Handler)
	e.Logger.Fatal(e.Start(fmt.Sprintf("0.0.0.0:%d", *port)))
}

I am getting the following error:

echo: http: panic serving [::1]:61803: runtime error: invalid memory address or nil pointer dereference
goroutine 21 [running]:
net/http.(*conn).serve.func1(0xc0000b21e0)
	/usr/local/go/src/net/http/server.go:1801 +0x147
panic(0x14f7460, 0x18bed00)
	/usr/local/go/src/runtime/panic.go:975 +0x47a
newform-api/inputform.(*ServerInterfaceWrapper).Externalhealthcheck(...)

API Definition files: