Append/modify same file in xbee file system

I am using XBee 3 RF module, I wanted to test the I/o file system. To test I used simple code where it will open file as an append mode and will write Hello World! and followed with file close in every 1 second interval but problem what I am facing is once file was opened in append mode next time to open the same file in append mode causing an os error as ‘EEXIT’ which means file already exist.
In Digi Xbee 3 user manual I went through file system limitation but I did not find any limitation regarding append/modify file

Below is the code for the above details. I wanted to know Is that possible to append/modify the file once again without removing or deleting
the file from file system?

NOTE: I used file as xbee.txt

import uio, uos

while True:
print(‘Open a file’)
with“xbee.txt”,mode=‘a’) as txt:
size = txt.write("Hello World!