The error “GSTIN is required for the Tax column, Please add GSTIN in the company settings or remove the Tax column from the file and upload again” denotes that you might not entered the GSTIN number in the company details, but in the downloaded template there is tax column present in it.
We request you to either add the company GSTIN & upload the sheet again or remove the “Tax” and “Price with Tax” column in the template and upload it again.