By PrestaTips 
Prestashop 9 is very good CMS, but sometimes you get quick little headaches… and messages and available resources not very clear! Me give you example error here, and how fix it!
Ask Google !
This first thing you do obviously. In our case results give various answers :
- forums
- blog articles (like here!)
- github issues
Overall it give this : “clear cache” “reconfigure your hosting”
We notice however that problem not new, with messages already dating from 2023 ! Problem not really sit on Prestashop side, even if message not very clear.
Ask Claude !
This where power of AI can help.
Claude invite you first to open inspector of your browser, then “Network”. And have also answer :
Answer unanimous : error 403 !
Here then personalized recommendations :
Ask hosting support directly (fastest): “I get 403 Forbidden (generic Apache page) on subdomain dev.mysite.fr when POSTing to /admin…/ajax with a source=https://… param, works fine on my other vhost mywebsite.fr/dev2026. Can you check ModSecurity/WAF logs for that subdomain around [timestamp] and whitelist that rule?” — give them exact failing request URL + timestamp, they can grep modsec audit log server-side (something Claude no can see from outside).
Self-check: if you have SSH/root access, look at /usr/local/apache/logs/modsec_audit.log (cPanel/CloudLinux typical path) or ask reseller panel for ModSecurity Tools app, filter by that subdomain, correlate timestamp.
Quick test yourself: temporarily disable ModSecurity for that one subdomain in cPanel → “ModSecurity” tool (toggle per-domain) if you have access, then retry upload. If it work, confirmed, then re-enable + ask host to add proper exception instead of leaving fully off.
Ask Your Host !
Since you pay expensive host with support, might as well they do work !
Hello,
Thank you for contacting Our super host.
We have disabled rule 123456 for domain dev.mysite.fr
It however possible another WAF rule trigger.
Could you perform new test and tell us if problem persist ?
Thank you.We test, it work ! Thank you Google, Claude and host !