This has already been reported on the release of SFOS 4.1. and also confirmed for 4.2. e.g.:
- Cannot check checkboxes in the captive portal browser
- [Release notes] Verla 4.2.0 - #112 by scharelc
one workaround is to open the browser and navigate to a non-ssl page such as: http://neverssl.com. This will redirect you to the captive portal of the wifi and you can probably click the checkbox and accept terms and conditions