I have some Python code that has successfully been making API calls for months (to specifically start a Workflow). It suddenly stopped working the week before last. When I went to investigate, the code that gets me an access token has suddenly stopped working, returning the normal error of {'error': 'invalid_grant', 'error_description': 'Grant credentials are invalid'}

My question is, is there some kind yearly “account refresh” I need to do? Or is there a backend token I am not aware of that needs a refresh? I did check and my client secret, client id, and service account id are all correct. 

Here is a simplified version of the code. 

def get_access_token(client_id_var, client_secret_var, service_account_id):
    #This URL gets us our access token
    # Define the URL
    url = "https://api.box.com/oauth2/token"

      # Define the request parameters
    payload = {
    "client_id": client_id_var,
    "client_secret": client_secret_var,
    "grant_type": "client_credentials",
    "box_subject_type": "user",
    "box_subject_id": service_account_id}

    # Define headers
    headers = {
        "content-type": "application/x-www-form-urlencoded"
    }

    # Send POST request
    #This sends all of the above information to box and in return it gives us our access token.
    response = requests.post(url, data=payload, headers=headers)
    response_json = response.json()
    print(response.json())
    access_token = response_jsons'access_token']
    return(access_token)


def create_header(client_id_var, client_secret_var, service_account_id):
    access_token = get_access_token(client_id_var, client_secret_var, service_account_id)
    headers = {
        'Authorization': f'Bearer {access_token}',
        'Box-Client-Id': client_id_var,
        'Box-Client-Secret': client_secret_var}
    print("Sucesfully Got the Access Token and Created the Header")
    return(headers)

And then I’d use the header to make the API Calls. Again, this worked successfully for months and I checked and my client id, secret, and account id have not changed.