Do you have any sort of security plugin active? It could be mis-configured. Unlikely since updating posts is a normal operation.
One common cause for such an error is overly aggressive modSecurity configuration. You’ll need your host to help you alter its configuration. Even if not modSecurity, it’s still most likely a server or network configuration issue of some sort that your host would need to help you resolve. The 403 is typically returned by the server before WP even gets involved.
@bcworkz thanks for your reply its fixed now I talked to namecheap helpdesk and the issue was with the Modsecurity.
They fixed it
Thanks for your help!
