Hello,
The following is generic bitcoind info (not specific to this plugin):
8332 is the default Bitcoin port for the RPC API, and 8333 is the default P2P post. For the purposes of communicating with WordPress, we are interested in the RPC port, i.e. 8332. Port 8333 should be open to let the wallet communicate with other wallets. Incoming connections to your wallet should be allowed on these ports, and that means that any firewalls that are in place should be open to the internet. You can use this tool to check: https://www.canyouseeme.org/
You mentioned a router. If you are on a home network, you will need to enable NAT on your router. i.e.: You need to add a rule that says that incoming TCP connections to 8332 or 8333 will be redirected to the 8332 or 8333 ports of your machine on your local network. Your machine on your local network will have a local IP that will most likely begin with 192. Your ISP cannot do this, only the person who is managing the router can. How you do this will depend on the exact router model and will be explained in the router’s manual.
Please understand that what you are doing is non-standard. I did not include any of the above information in the guide, because most people who install a full node will either already know networking, or would not be installing the wallet behind a local network; the usual setup is with an internet-facing server. I might create another guide on how to setup a full node on a local private network.
In any case, what you are trying to do is doable. Check your port first, to see that it is open from the machine that runs WordPress. Once this is done, then you can configure the coin adapter.
with regards