Reply To: DataTables warning: table id=si-data-table – Invalid JSON response. For more inf

[RRowley]

This is the same error that you had before. As if the items you deleted from the invoice_item_tax table, were not deleted. Here is an example of a SQL DELETE statement for multiple records at a time:
DELETE FROM si_invoice_item_tax WHERE invoice_item_id IN (1354, 1355, 1356, 1357);

Not sure how if you deleted these records before, they still show up. But you should verify that once they are deleted, an inquiry no longer finds one or more of them. Delete the php.log file and run SI again. Hopefully, you will be past this error.