Why I am not able to upload my InDesign file? I keep getting Error 12 and Soap 1.1

The text of the error message will often contain a line like this: "The byte 0x13 is not valid at this location." Note that the numbers may be different on the exact error you see, this is still the same type of error. 
There can be several reasons behind this error, however most of the time it happens because of the formatting of the text that has been added to the file while creating it in InDesign. It happens generally because of the presence of non-ASCII Unicode characters in the field names or prompts assigned on the document with the plugin. You can replace it with plain text. If this does not resolve the issue, then please create a new support ticket here and we will investigate it for you.