This call to Prestashop Web Services failed and returned an HTTP status of 401. That means: Unauthorized
500 Internal Server Error upon entering module configuration page FAQ. Best tools for PrestaShop ➜ MyPrestaModules.com
SOLVED] Module manager 500 Internal Server Error - Addons, modules and themes developers - PrestaShop Forums
Prestashop backend upload image failed solution (500 ERROR and attempted to call function "imagecreatetruecolor" from the global namespace) | Unicoq - IT Consulting Firm
Prestashop Error 500 - Top 7 reasons, and how to fix them