As noted on the blue button that is greyed out and the text above, there is a minimum of 20 images for the DJI specific workflow. The button will tell you how many more images you need.
If you have less than 20 images it is likely that there is either very thin overlap or the area is very small.
The workaround for this is to include copies of your images to meet the 20 image minimum. Uploading duplicate images is a goofy workaround but it works.