[InputMetaDataXml] : The 'Fields' is invalid. Input string was not in a correct format.

In Nintex workflow if you are trying to upload a document by using “Office 365 upload file” and trying to add value in person (user) field. You may encounter the following error “[InputMetaDataXml] : The ‘Fields’ is invalid. Input string was not in a correct format.” The solution is quite simple, you need to map the “User Id” in the “Advanced Lookup” option. Continue reading [InputMetaDataXml] : The 'Fields' is invalid. Input string was not in a correct format.