I am trying to add more than one document to my attributes, but it does not allow me.
If you want to add more than one document to a task, you have to change the configuration of the task attribute.
In Signavio Explorer click on "Setup" → "Define notations / attributes"
Create a new document attribute.
Select data type "Document/URL" and check "As list".
Then go to your diagram and upload your documents.
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