You have two options:
- Delete some of your account's existing items in order to free up sufficient "resources"
- Purchase a plan that provides more resources
The required and available available are listed on the section of the page under that tooltip:
I can't see for certain because the tooltip is partially covering the information, but it appears the reason you were unable to use the Template is because you have used up your plan's allocation of Things. When you use the Template, it automatically creates a Thing. So if you deleted one of your existing Things, you would then be able to use the Template.
You can see the list of your existing Things here: