victogranados96 From the screenshot you attached, there are a number of red boxes marked "MISSING" in the viewport. This means that Spine cannot find the correct image set in the attachment's image path.
An attachment's image path can be found in the properties displayed at the bottom of the Tree view when the attachment is selected, as shown in the following image:
The image path of the attachment is combined with the images path, which can be found when the `Images' node is selected in the Tree view, like the following image:
In this example, the images path is . /images/, so the eye-indifferent attachment refers to the image named "eye-indifferent" in the folder named images, which is located in the same folder as the Spine project.
Importing skeleton data (in your case, the .json file) does not set the images path, so if you do not set the images path, the image path for each region or mesh attachment will be incorrect and they will be marked as MISSING. In this state, this error occurs because the correct images cannot be found when packing the texture atlas of the skeleton.
Therefore, please fix the images path or image path for each attachment so that the correct images are displayed in the viewport before exporting your skeleton.
The following blog post may be helpful for you:
Blog: Importing skeleton data
