The loop value must resolve to a 'list', not 'str'

TASK [matomo : Ensure that matomo_site_urls start with http(s)://] ************************************************************************************************************************************************
[ERROR]: The `loop` value must resolve to a 'list', not 'str'.
Origin: /home/chris/webarch/servers/galaxy/roles/matomo/tasks/add_site.yml:28:13

26           - ( url is regex("^http[s]*:\/\/.*$") )
27         quiet: "{% if ansible_verbosity == 0 %}true{% else %}false{% endif %}"
28       loop: "{{ matomo_site_urls }}"
               ^ column 13

Provide a list of items/templates, or a template resolving to a list.

fatal: [example.co.uk]: FAILED! => 
    msg: The `loop` value must resolve to a 'list', not 'str'.