Working Well (but check API keys)

Have used Mailchimp version in the past. Worked well.

Struggled with Campaign Monitor version but errors were related to user input (possible reason for bad reviews suggesting it doesn’t work).

Campaign Monitor isn’t intuitive so make sure you grab the right Client API not the Admin API key and for the List ID, follow these instructions – https://createform.com/support/campaignmonitor-list

Thanks Renzo for helping me through this.