Error – JSON

When I try to save the page with the shortcode (Designer with content:
<pre id="block-d9771316-264e-4602-b84f-0ce895915a6d" class="wp-block-preformatted block-editor-block-list__block wp-block is-selected rich-text block-editor-rich-text__editable is-hovered wp-block" role="textbox" aria-label="Write preformatted text…" data-block="d9771316-264e-4602-b84f-0ce895915a6d" data-type="core/preformatted" data-title="Preformatted">[product_designer])

I get the following error on updating:
Updating failed. The response is not a valid JSON response.

If i go to that page, I get this error:
Product is not selected. this is probably issue with site permalink settings, please select \"Post name\" on permalink settings

Whereas my permalinks are set to post-name.

Please assist.</pre>