How to send a POST request with after create or update of a user (RAILS)

Question

This is my first time working with Requests and i'm a little confused, any guidance would be greatly appreciated.

Task: after a user is created i would like to send that user's information (name, email, etc) to another site that we are integrating with. The goal is when a user leaves our site and goes to the next site (we're also setting up SSO) they would see the same information.

Here is what I put in the Model:

  after_validation :send_new_user_to_hivebrite, on: [ :create, :update ]

  def send_new_user_to_hivebrite
    
    payload = {user:{email:Email.find_by(person_id:self.id).address,sub_network_ids:[0],firstname:self.given_name,lastname: self.family_name,is_active:true}}
      
    begin
      response = RestClient::Request.execute(
        method: :post, 
        url: 'https://mysite.us.hivebrite.com/api/admin/v1/users',
        payload: payload.to_json,                  
        headers: {content_type: :json, accept: :json, Authorization: 'my_token'}
      ) 
      self.description = "Response code: #{response.code}"
    rescue RestClient::ExceptionWithResponse => e
      self.description = "It didn't work"
    end

  end

I tried doing the same thing but with a GET request (without the payload) and stored the response in self.description and it worked. so the authorization works and the url works. which means something is wrong with my payload right? am i formatting it wrong? this exact format worked in postman:

{
  "user": 
    {
        "email": "[email protected]",
        "sub_network_ids": [ 0 ],
        "firstname": "Moe",
        "lastname": "Test",
        "external_id": "test_person_id",
        "sso_identifier": "test_identifier",
        "is_active": true,
        "headline": "Nothing to fear, POSTMAN is here",
        "summary": "This is my test summary, you will only see it if this post request worked!"
    }
}

I thought maybe it couldn't find the email because it was not created yet or something, so i tried updating an existing user and it still goes to rescue.

In rails C i did

payload = {user:{email:Email.find_by(person_id:Person.last.id).address,sub_network_ids:[20548],firstname:Person.last.given_name,lastname:Person.last.family_name,is_active:true}}

then i did

irb(main):016:0> payload.to_json
=> "{\"user\":{\"email\":\"[email protected]\",\"sub_network_ids\":[20548],\"firstname\":\"temp\",\"lastname\":\"tempsir\",\"is_active\":true}}"

I checked https://jsonlint.com/ to see if that is valid json and it was. sooo what am I doing wrong?