Hi,
I don't know why you would have that error. Maybe your server has some kind of protection system and is blocking the saving for some reason.
What I can recommend as an alternative is to install and configure this PayPlug v2 plugin:
It uses the latest API from PayPlug and is compatible with the DSP2 directive:
www.latribune.fr/entreprises-finance/ban...est-quoi-764449.html
This new Paylug plugin will be added in the next version of HikaShop and doesn't require the creation of a payplug_parameters.json file like the old one needed. So hopefully, it will circumvent the problem.