passing form values to cfhttp request as comma delimited

hi experts. too much beer and my lost mind. i have a form field. a select menu where i can select multiple items. on the click of a button, i want to pass the selected items as a comma delimited list. i am confused, i tried using a loop but it failed:

here is what i tried.

<cfloop list="form.selectusers" index="k">
  <cfhttp url="http://smslane.com/vendorsms/pushsms.aspx?user=abc&password=xyz&msisdn=#k#&sid=WebSMS
&msg=#form.message#&fl=0"></cfhttp>  
</cfloop>
 
but i want to pass something like this:
 
  <cfhttp url="http://smslane.com/vendorsms/pushsms.aspx?user=abc&password=xyz&msisdn=996734673,99374673,7364387483&sid=WebSMS
&msg=#form.message#&fl=0"></cfhttp>  
 
like multiple mobile numbers using comma separation. how can i do that. plea guide me

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