Have a free local wi-fi network and want to expand it just a bit.

Can't seem to figure out how to get a router to connect because of the captive portal where you gain access to the internet.

I've seen solutions for hotel wifi and travel routers but I'm going to set this up as a permanent solution.

Going to have to buy new hardware anyway but looking for a solution?

I have this one and it will do what you want which is repeater mode.

https://www.amazon.com/dp/B07712LKJM

Great thanks!

Follow up question. How hard is it to connect the router to a network that has a splash page/captive portal log in?

It varies. One trick I've used if it's not coming up is try to load this site http://neverssl.com/ in your browser and that will often cause the portal page to load.