Upload zip of your creative. It should have one html along with assets (i.e js, css, images, fonts etc).
Enter url of your creative.
Enter width of creative between 10 and 1280.
Enter height of creative between 10 and 720.
Select the loop.
Enter duration of creative in seconds. If your creative has loop then enter duration of only single loop.
Enter the value 0 second. Use this option in your second attempt of conversion. In case if you see "partially loaded image at the begining of GIF", or "some kind of white or gray patch at the begining of GIF", or "loader of your animation", then you can specify a short delay. Tool will wait for specified time and will start capturing. For example you can specify 0.5 or 1 or 2 second(s).
Select your interest for automatic selection of Quality and Frames per second.
Select the value in which creative to be recorded.
Select the value in which GIF has to be animated. Ideally value should be same as Capture frames per second. If you want to reduce file size further, then capture animation in less frames per second and animate in little bit higher frames per second. For example you can capture your creative in 8 FPS and animate in 10 FPS. This will result smoother animated GIF with slightly lower file size.
Select the quality. File size of GIF is depend upon the Quality.