Hi ,
1. Please access IAP via CLI & run the following command:
show captive-portal-domains
Eg:
IAP# show captive-portal-domains
Internal Captive Portal Domain:
securelogin.hpe.com
2. Edit the cloud guest page
Central UI- Guest Access-Splash Page- Edit the page
Change the parameter shown in the attached screenshot to the output shown for "Internal captive portal domain" in the 1st command & save the config.
Please try post the same.