H'm, still having troubles understanding the problem.
Let me get this straight:
You connect yourself with a PC to repeater1 - you use the voucher and it works.
Now, you move on to the next repeater, call it repeater2, and you have to re-authenticate again, with a new voucher. Is that right ?
Can you tell me what your IP was when you connected yourself to the portal when you were using repeater1 ? What is your IP when you use repeater2 ?
Btw: normally, to make things simple to work with, you have some work to do.
Behind the Portal-interface-NIC, you hook up a switch. On this switch, you hook up - by cable - all your wifi access points, and theses boxes should work in AP (Access Point) mode. These AP's should have their DHCP server function shut down. Never use the WAN ether net port on these devices (if one is present). I have many 'DD-WRT' on WRT54GL working like this for the last 10 years.
Using repeater might change the IP …. this messes up the portal authentication.
Using repeater might change the the MAC .... this messes up the portal authentication.
"Repeaters" are nice boxes, but you only use one if nothing else is possible. You only move the 'cable' problem to a 'logical network' problem.
Btw: I had some good experiences with AP-boxes using "WDS" mode.