'Hsn' Must Not Be Empty

In this error you need to check HSN code is entered or not in uploading file.

Also HSN should be valid that is entered.

Also find Steps to check HSN Code of your product and Services:
Step 1: Open e-way bill portal Step
Step 2: Go to 'Search'
Step 3: Select 'Product & Services'
Step 4: Enter HSN code or Name of product & Captcha
Step 5: Clicks 'Go'
Please go through the following link
For EWay Bill https://ewaybillgst.gov.in/Others/ProductSearch.aspx
For Einvoice site https://einvoice1.gst.gov.in/Others/Product

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