A couple of things. One I believe that "HTML and Text", is suppose to go out as one email, and the reader or software decides which one to read, you not suppose to send 2 emails. 

ANd the Variables  on a "TEST" messages going to one person, DO not work. $[FIRST||] , doesn not resolve AND these links do not point to a webpage, but maybe they shouldn't because its a test.

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Also in your help files, you should probably describe what happens if the field is blank, I thought "Customer" would appear

https://zoho-campaign.wiki.zoho.com/Use-Merge-Tags.html

$[FIRST||]