Example searches: “external_references”, “postcode”, “provider_reference”, “groups”, “updated_at”
Optional parameter. UUID The UUID of the custom field
curl \ --request DELETE 'https://api.plannrcrm.com/api/v1/custom-field/6ff8f7f6-1eb3-3525-be4a-3932c805afed' \ --header "Authorization: Bearer $ACCESS_TOKEN"