Trying to post video on Dtube having thumbnail Error

So I been having troubles trying to download video onto Dtube.

Step 1. Load video which goes through fine shows video

Step 2. Is where I am having troubles it’s says thumbnail file is too big. I made multiple thumbnails even tried changing image size. I also downloaded Firefox to see if that would work after doing a bit of research.

Now here is what I keep getting after trying to click on add snap or take snap

I tried clicking on taking snap after video loads and it take me to my browser with an image from my video. Nothing loads it just stays on the image. When I go to return back to the previous page , everything that I had input is now gone or deleted causing me to start the process over. This process has been very frustrating and I can’t seem to get a thumbnail.

Step 3. Title works fine

If anyone can help me with a solution I will greatly appreciate it! By the way I am using a iphone 7s plus and a MacBook Pro.