Business rules or CPM which gets triggered first?

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Hi,

I would like to know which gets triggered first a CPM or Business rule?

I am setting the email id of a contact in incident create CPM and wrote a business rule to send an acknowledgment email to the contact using "Send Receipt Email" action, which is not getting triggered as of now.

Within incident create CPM i am setting a contacts email id and also a incident custom field value to yes and in business rule i am checking for the custom field value change and gave "Send receipt Email" as action. but mail is not getting triggered.