Container’s number have official format number, with a combination of 4 letters and 6-7 numbers, for example ABCD123456. If you do not input the numbers in this format, you will receive an “invalid value” error. 

In case, your container number does not match with the standard official format, or you have your own container number, then you can add 4 letters, in front of your numbers. 

Example can be: "XXXX123456” or “ABCD123456”.