Thanks for the screenshots to understand your issue. I have checked your issue on your site. Actually, The 403 Forbidden error means that your server is working, but you no longer have permission to view all or some of your sites for some reason. I have created a test product on your site named “Support Testing” and it was added and updated successfully as you can see in this video. https://www.loom.com/share/806b33eaf2c14e91a753608f889d353b?sid=be0295f8-c384-472e-9058-4d26bf28fc2d
The issue appears only in the existing products. Please check this article to understand why this error appears and how to fix it: https://wordpress.org/support/topic/403-on-product-update/#:~:text=The%20403%20Forbidden%20error%20means,htaccess%20file.