Pagination not working in Python Session.put() - python-3.x

Question

I am trying to upload a file to a website (that has an inbuilt API) using the following code. The code reads a list of medical codes/diagnoses codes etc. (1 column in a text file) and uploads it to the required page.
Issue:
After uploading the file, I noticed that the number pages is not coming out properly. There can be up to 4000 codes (lines) in the file. The code list page in the website will show 20 lines per page, which means, I would expect at least 200 pages to be there after uploading. This is not happening. I am not sure what is the mistake that I am doing.
Also, I am new to Python (primarily SAS) and have been working on automating bits and pieces of code. One such automation is this exercise. Here, the goal is to upload multiple files to the said URL. Today the team is uploading them one by one manually. With the knowledge I picked up from tutorials and other sources, I was able to come up with this.
import requests
import json
import os
import random
import pandas as pd
import time
token = os.environ.get("USER_TOKEN")
user_id = os.environ.get("USER_ID")
user_name = os.environ.get("USER_NAME")
headers = {"X-API-Key": token}
url = 'https://XXXXXXXXXXXX.com/api/code_lists'
session=requests.session()
cl = session.get(url, headers=headers).json()
def uploading_files(file,name,kind,coding_system,rand_id):
df = pd.read_table(file, converters={0:str}, header=None)
print("Came In")
CODES = df[0].astype('str').tolist()
codes = {"codes": CODES}
new_cl = {"_id": rand_id, "name": name, "project_group": "TEST BETA", "kind": kind,
"coding_system": coding_system, "user": user_id, "creator": user_name, "creation_method": "Upload", "is_category_mapping": False,
"assoc_users": [], "global": True, "readonly": False, "description": "", "num_codes": len(CODES)}
request_json = json.dumps(new_cl)
print(request_json)
codes_json = json.dumps(codes)
print(codes_json)
session.post(url, data=request_json)
session.put(url + '/' + rand_id, data=codes_json)
text_Files= os.listdir(r'C://Users//XXXXXXXXXXXXX//data')
for i in text_Files:
if ".txt" in i:
x=i.split("_")
file='C://Users//XXXXXXXXXXXXX//data//' + i
name=""
for j in i[:-4]:
if j!="_":
name+=j
elif j=="_":
name+=" "
kind=x[2]
coding_system=x[3][:-4]
rand_id = "".join(random.choice("0123456789abcdef") for i in range(24))
print("-------------START-----------------")
print("file : ", file)
print("name : ", name)
print("kind : ", kind)
print("coding system : ", coding_system)
print("Rand_Id : ", rand_id)
uploading_files(file, name, kind, coding_system, rand_id)
time.sleep(2)
print("---------------END---------------")
print("")
break ''' to upload only 1 file in the directory'''
Example data in the file (testfile.txt)
C8900
C8901
C8902
C8903
C8904
C8905
C8906
C8907
C8908
C8909
C8910
C8911
C8912
C8913
C8914
C8918
C8919
C8920
C8921
C8922
C8923
C8924
C8925
C8926
C8927
C8928
C8929
C8930
C8931
C8932
C8933
C8934
C8935
C8936
C9723
C9744
C9762
C9763
C9803
D0260
Sample Data Snapshot
Wrong Representation
Expected