On both switches, it is required to have a single route to the TFTP server (By default this is 10.92.100.60, but individual configurations may differ).
(switch#)
show ip route 10.92.100.60
Example output:
Displaying ipv4 routes selected for forwarding
'[x/y]' denotes [distance/metric]
10.92.100.60/32, vrf default, tag 0
via 10.252.1.9, [70/0], bgp
10.252.1.9 is pingable.