Had an issue where my url worked fine, and it had "Ad Tracking ID" in it, but I took it out for a bit to test some things on the channel, then went to put it back in and it said it (now) also needed "Ads Limit Tracking" now too. Or something like that, might've been vice versa. but the url had things like "_ADS_TRACKING_ID_" in the string.
Could be something like that where Roku accepted legacy urls, but won't allow new ones going forward. Maybe try getting in touch with firstname.lastname@example.org
if you can. Just happened this week for me as well but I haven't reached out yet, debating just reverting back to RAF.