Why is a sending multimessage box poping up before I will send a picture message?

[AC Question]

a box pops up when trying to send a picture message instead of it just putting the picture in the text box so i can write a caption under the pic when sending and when it does this some ppl don't receive the picture message

 

[B. Diddy]

Welcome to Android Central! Which phone, and which messaging app? Is your mobile data turned on? What does the popup box say?