Command:
ssh -i '/home/daijwgmi/.ssh/trappist1_main_key' -o StrictHostKeyChecking=no 'python'@'192.64.115.78' "python3 '/home/python/echo_test.py'" 2>&1

Output:
python3: can't open file '/home/python/echo_test.py': [Errno 2] No such file or directory