Problem
All the users targetted via an Email campaign were removed due to personalization failure.
Cause
As the personalization was based on custom attribute 'First Name', personalization of this campaign failed as it was looking into MoEngage tracked attribute 'First Name' and as this attribute did not exist for any of the users in segment, personalization failed.
Personalization Code: {{UserAttribute['First Name']|default('MOE_NOT_SEND')}}
As the frontend/readable name of both the attributes i.e custom attribute 'First Name' and MoEngage Tracked attribute 'First Name' is the same, the personalization resolves to look into MoEngage tracked attribute and not the custom attribute.
Solution
It is not recommended to track custom attributes with same names as the MoEngage tracked attributes as these are reserved keywords. Though we would be able to track this data on user profile, you would face an issue when personalization is done based on these attributes.
List of MoEngage tracked attributes:
1) Name
2) First Name
3) Last Name
4) Birthday
5) Gender
6) Location
7) Mobile Number
8) Email
9) ID
10)Advertising Identifier