Using field from DE in SMS message

Question

I have a question. I have two options of SMS message creating

1. Use AMPscript like in email building

%%[
var @fname
set @fname = [First_Name__c]
%%]
%%=v(@fname)=%%

%%[
var @row, @rows, @fname
set @rows = LookupOrderedRows("SMS",1,"StartDateTime desc", "Phone__c", MOBILE_NUMBER)
set @row = row(@rows,1)
set @fname = field(@row,"First_Name__c")
%%]
%%=v(@fname)=%%

Why for the first option SMS didn't come but for the second it came? Journey settings for both variants were equal. Or why we cant use 1st option for sms message?

Answer 1

The First_Name__c must be in your send context for the personalization string to be valid. You can use AttributeValue to validate existence of the contextual string. This'll illustrate the function by returning Friend if First_Name__c cannot be found.

%%[

set @fname = AttributeValue("First_Name__c")
set @fname = iif(empty(@fname), "Friend", @fname)

]%%
%%=v(@fname)=%%

In the second one, MOBILE_NUMBER is a system string that's present in the send context. It's available since it's bound in Contact Builder. I'd update your code to have a fallback value as well:

%%[

set @rows = LookupOrderedRows("SMS",1,"StartDateTime desc", "Phone__c", MOBILE_NUMBER)

if rowcount(@rows) > 0 then
  set @row = row(@rows,1)
  set @fname = field(@row,"First_Name__c")
else
  set @fname = "Friend"
endif

]%%
%%=v(@fname)=%%