request post with retrofit in android-CodePudding

I want use request post in my app. I used this but I have a problem. I face this problem when I want to create an account.

status code 403

You can see my code:

Api.kt

interface Api {
@Headers("Content-Type: application/x-www-form-urlencoded")
@POST("users/signup")
@FormUrlEncoded
fun createUser(
    @Field("first_name") fName: String,
    @Field("last_name") lName: String,
    @Field("email") email: String,
    @Field("username") username: String,
    @Field("password") password: String,
) : Call<UserResponse>
}

UserResponse.kt

data class UserResponse(
val email: String,
val first_name: String,
val password: String,
val last_name: String,
val username: String
)

SignUpActivity.kt

binding.btnSignUp
        .setOnClickListener {

            val username = binding.etUsername.text.toString().trim()
            val password = binding.etPw.text.toString().trim()
            val fName = binding.etFName.text.toString().trim()
            val lName = binding.etLName.text.toString().trim()
            val email = binding.etEmail.text.toString().trim()

            if (username.isEmpty()) {
                binding.etUsername.error = "Password required"
                binding.etUsername.requestFocus()
                return@setOnClickListener
            }

            if (password.isEmpty()) {
                binding.etPw.error = "Password required"
                binding.etPw.requestFocus()
                return@setOnClickListener
            }

            val logging = HttpLoggingInterceptor()
            logging.level = HttpLoggingInterceptor.Level.BODY

            val httpClient = OkHttpClient.Builder()

            httpClient.addInterceptor(logging)
            val instance: Api by lazy {

                val retrofit: Retrofit = Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .client(httpClient.build())
                    .build()
                retrofit.create(Api::class.java)
            }
            instance.createUser(fName, lName, email, username, password)
                .enqueue(object : Callback<UserResponse> {
                    override fun onFailure(call: Call<UserResponse>, t: Throwable) {
                        Toast.makeText(applicationContext, t.message, Toast.LENGTH_LONG).show()
                    }

                    override fun onResponse(
                        call: Call<UserResponse>,
                        response: Response<UserResponse>
                    ) {
                        Toast.makeText(applicationContext, response.code(), Toast.LENGTH_LONG)
                            .show()
                    }
                })

        }

I use this request on postman and it works good

Happy Coding :-)