this should do the job

eive_tmtc/tmtc/payload/ploc_mpsoc.py

@@ -503,15 +503,18 @@ def prepare_cam_take_pic_cmd(object_id: bytes) -> bytearray:
     return bytearray(command)
 
 
-def prepare_simplex_send_file_cmd(object_id: bytes) -> bytearray:
+def prepare_simplex_send_file_cmd(object_id: bytes) -> bytes:
+    num_of_chunks = int(input("Please specify the number of chunks: "))
+    assert num_of_chunks >= 0
     filename = input("Specify filename: ")
     command = (
         object_id
+        + struct.pack("!I", num_of_chunks)
         + struct.pack("!I", ActionId.TC_SIMPLEX_SEND_FILE)
         + bytearray(filename, "utf-8")
         + bytes([0])
     )
-    return bytearray(command)
+    return command
 
 
 def prepare_downlink_data_modulate_cmd(object_id: bytes) -> bytearray: