Google Doc Template: Selected document does not have any image

I am trying to generate a PDF from Airtable using a Google Doc Template.
The template is one page long and has 6 images and three texts. I want to change images from Airtable instead the ones that are in the template. When I load the Google Doc Template, I receive a message that there is no images inside the template. I try different ways of inserting the pictures in the template and also I make sure that the images are PNG.

Any one can tell me how to fix this? Many thanks in advance!

This is the template: