I am trying to set up UPNP to allow P2P connections between networks. When I attempt to addportmapping, I get error code 26. Upon checking all discovered devices, I get isvalidgateway = false. I'm not sure what exactly I'm doing wrong, though I suspect it might have to do with my peculiar networking setup. I have a modem/router combo provided by my ISP which does not offer a bridging mode for disabling the router, and a TP-link deco mesh system connected to it to provide wifi for the house.
Could this be the cause of my issues? Any suggestions on how to fix it? While I'm tempted to plug directly into my ISP's router, I'd like to see if there's a way to solve as is, in case this is a semi-common use case.
Edit: The weird network setup does appear to be the problem; I connected my computer directly to the ISP router and it worked. Still, I'm wondering if there's anything i could have done, again in case someone else runs into this issue. Thanks!