It looks like you are working on the Adobe's AEM WKND Project. You might be missing out the editable template's policies. You need to set some allowed components in the responsive grid component. Don't forget to unlock the component from the editable template after changes are made, so the JCR node's editable property is set to true (this allows authors to add components to the page).
By following this document, you would be able to go step by step on how to allow components for a specific editable template: https://docs.adobe.com/content/help/en/experience-manager-learn/getting-started-wknd-tutorial-develop/pages-templates.html
If you are working with static templates, then it from the editable page, go into design mode; add allowed components in this section.
I hope this helps.