Wifi network not combined after 802.11r ft(roaming) is set

i am using TP-Link Archer C6 v3 as a main router and Haier HAR-20S2U1 as a signal extender. both are on openwrt.
as i dont want to use my signal extender as traditional repeater as it will display two separate WiFi networks, i want to use 802.11s mesh to provide internet access to secondary WiFi, and 802.11r FT for combining WiFi network as one.
but even after setting up 802.11r, the WiFi network list from other device(i.e. smartphone) still shows me two separate networks and does not change connection from each other. what am i doing wrong?
here's the setup

  1. Main AP Master
  • auth: WPA3-SAE
  • KRACK countermeasures: enabled
  • WMM Mode: enabled
  • Country Code: KR
  • Channel: 44
  • Standard: 802.11ac
  • Width: 80MHz
  • 802.11r FT: enabled
  • Mobility Domain: 1716
  • FT Protocol: FT over DS
  1. Main AP Mesh
  • Mesh ID: (it is a secret)
  • Encryption: WPA3-SAE
  1. Secondary AP Master
  • auth: WPA3-SAE
  • KRACK countermeasures: enabled
  • WMM Mode: enabled
  • Country Code: KR
  • Channel: 44
  • Standard: 802.11ac
  • Width: 80MHz
  • 802.11r FT: enabled
  • Mobility Domain: 1716
  • FT Protocol: FT over DS
  1. Secondary AP Mesh
  • Mesh ID: (it is a secret)
  • Encryption: WPA3-SAE