PPPoE server routing problem

Dear guys!
I have configured a Mikrotik core router as PPPoE Server that acts as a concentrator for our WiFi clients that have a router (Linksys, D-Link, etc) configured as PPPoE Client.
Our clients have a public IP on WAN interface of their router and a private IP on LAN interface, then on router is configured NAT. With this configuration all works fine.

But if disable NAT on clients router and set a public IP of a /30 or /29 network on LAN side of router, our clients can’t surf to internet and from PPPoE Server I can’t ping IP address that I have assigned to LAN side of client router: why? On PPPoE server there is a /30 network route but however ping fails (See attachment)

Could you help me please?

P.S.-> sorry for my english

Thanks in advance

Best regards
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