The first think you wanna do is add 1 (which is the maximum if you don't have imgflip pro) text on to a gif. Then, generate what you already have as a gif even if there is only 1 out of however many texts you want (I'm gonna call this gif 1), and once you do that you have the option to download gif 1, which you are going to do. The next step is to go to gif maker and upload gif 1 so you can caption it again. Then you can put another text and repeat the process however many times. In fact this is what I did to add more than one text on here
