DKIM and cmap

does anyone know much about adding a DKIM record to a domain name?
Campaign monitor wants a DKIM record added but when I go https://dkimcore.org then try to their output in cloudflare I get an error (1004).
I’m adding it as a text record (as per the CF instructions https://support.cloudflare.com/hc/en-us/articles/360019093151) and I’ve tried a number of options for TTL but I get the same result.
I’ve never done it before so I’m probably doing something wrong
any ideas?

Can you post a screenshot of what you’re trying?

I’m familiar with that screen, and have several DKIM records of my own, but your screenshot shows no data for me to check.