Require agreement to terms on membership renewal

Is there a way to set up a checkbox that a member has to check to agree to T&C on membership renewal? We do it on registration, but I can't find a way to do it for every renewal. TIA.

Yes, within CBSubs > Settings > Display > Baskets in the "Terms and Conditions on checkout" section you can enable terms and conditions for payments.

Thanks.
I have done this. We have two items as Terms and Conditions for registration. When I go to renew and I click on Terms and Conditions, it doesn's display either of them. Instead the modal box displays the home page.

Generally that means the URL supplied isn't properly linked to your terms and conditions page. I recommend always making a menu item for things like this. So for example a Joomla article menu item. Next link directly to that menu item and add ?tmpl=component (begin with & if there's other params already on the URL) to the URL so it just shows the article inside the modal window.

I tried that, and it didn't work. 

I simplified it by having only one Terms and Conditions Field. The url points to a hidden menu, and I added the ?tmpl=component to it

When I inspect the link to show T&C, the url in the iframe is the site home page, and not the url in the T&C field. Everything is fine in the registration page.

Ensure your menu item should be public and published. The article itself should also be published and public. I recommend linking to your article as non-SEO and beginning with index.php. Example as follows.

index.php?option=com_content&view=article&id=ARTICLE_ID_HERE&Itemid=MENU_ID_HERE&tmpl=component

Replace ARTICLE_ID_HERE with the id of the article you're using for your terms and conditions. Replace MENU_ID_HERE with the id of the menu item linking to your article. Doing this will prevent in weirdness in Joomla's routing system and guarantee navigation to the article.