Hey there!
The error message most probably stems from the fact that the gallery shortcode cannot locate the images form the image source you’ve indicated – it is difficult to tell more precisely, as I do not see the back-end code. What I’d suggest you do is replacing this project with a new one that has the format “Gallery”, to which you can attach several images that will constitute the gallery, and include the text you need (i.e. “Click here to find out how to use our bags”) on the first image of the gallery, as a part of the image.
Sincerely,
Andrii / Satori Studio