Which of the following is not supported by FlexVPN?

A. NHRP

B. dynamic routing protocols

C. connectivity over public transport networks

D. IKEv1

E. connectivity to non-Cisco routers

F. IKEv2

Explanation:
Internet Key Exchange version 1 (IKEv1) is not supported by FlexVPN. FlexVPN supports only IKE version 2 (IKEv2). By contrast, Dynamic Multipoint Virtual Private Network (DMVPN) supports both IKEv1 and IKEv2.

FlexVPN is a standards-based VPN technology that simplifies the deployment of site-to-site, remote-access, hub-and-spoke, and spoke-to-spoke topologies. Because FlexVPN is standards-based, it supports connectivity to both Cisco and non-Cisco routers. Like DMVPN, FlexVPN uses Next-Hop Resolution Protocol (NHRP) for spoke-to-spoke communication; however, unlike DMVPN, FlexVPN spokes do not have to register with the hub. Unlike Group Encrypted Transport (GET) VPN, FlexVPN can be used to provide connectivity over public transport networks, such as the Internet. FlexVPN also supports dynamic routing protocols, dynamically addressed spoke routers, Quality of Service (QoS), and Network Address Translation (NAT).

Reference: https://www.cisco.com/c/en/us/products/collateral/routers/asr-1000-series-aggregation-services-routers/data_sheet_c78-704277.html
https://www.cisco.com/c/dam/en/us/products/collateral/ios-nx-os-software/enterprise-class-teleworker-ect-solution/prod_brochure0900aecd80582078.pdf (PDF)