Unexpecte or invalid content

When I add this code to the table tag WordPress throws up a warning that “This block contains unexpected or invalid content” and there is no option to “ignore”. The table gets greyed out and I am unable to edit the table further. I need the table to be editable in block mode with the tools for adding rows available because the (non thech savvy) site editor needs to be able to easily add rows to expand the table. Converting to classic or html breaks it for him.