Can't sign in to cloud stores with SAML using custom domains, When try to access the custom domain URL get the error "Unable to Process Your Request, There was an unexpected error" .

Custom domain configuration incorrect.

It is recommended that you migrate to the new SAML v2 configuration, which does no require special configuration for custom domains. For more information, see docs.

If you remain on the V1 solution:

1. Sign into Citrix Cloud at https://citrix.cloud.com.
2. From the Citrix Cloud menu, select StoreFront Cloud and then select Access.
3. On the Access tab, under stores, select your custom domain and edit.
4. Validate the SAML Application Configuration (Legacy SAML Config). if the the SAML App URLs are not correct update as below.

• In Identity Provider Entity ID for custom domain, enter the Entity ID from the second SAML application
• In SSO service URL for custom domain, enter the SSO URL from the second SAML application.
• In Logout URL for custom domain, enter the SLO URL from the second SAML application

Can't sign in to cloud stores with SAML using custom domains

https://docs.citrix.com/en-us/citrix-cloud/citrix-cloud-management/identity-access-management/saml-identity-custom-domain#dual-saml-application-configuration