Problem
All the users targeted via an Email campaign were removed due to personalization failure.
Cause
As the personalization was based on the custom attribute 'First Name', personalization of this campaign failed as it was looking into MoEngage tracked attribute 'First Name' because this attribute did not exist for any of the users in the target segment.
Personalization Code: {{UserAttribute['First Name']|default('MOE_NOT_SEND')}}
As the readable names of both the attributes i.e custom attribute 'First Name' and MoEngage Tracked attribute 'First Name' are 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 (Standard)
8) Email (Standard)
9) ID
10)Advertising Identifier