wait wdym?
I'm getting confused with the multiple configs posted here. It doesn't help that I was replying on a phone, making it difficult to tell which one is active at the moment. Sorry for adding more smoke than light.
All I can figure now is that what I take to be the current version of the dstnat rule:
add action=dst-nat chain=dstnat dst-address=wanip dst-port=3000 log=\
yes protocol=tcp to-addresses=192.168.88.243 to-ports=3000
…is referring to the literal string "wanip", which the router doesn't know how to look up. Either that needs to be a statically-assigned PPPoE public IP, or you need to refer to the interface instead:
add action=dst-nat chain=dstnat in-interface=pppoe-out3 dst-port=3000 log=\
yes protocol=tcp to-addresses=192.168.88.243
That formulation is more flexible anyway.
Note that you don't have to give "to-ports" when it's the same as dst-port. That's the implicit default.
By the way, where's your firewall? If this is a public-facing router, you shouldn't be without one.