Having added a payment method you need to go to the iTunes Store or the Music App as applicable: authorise your computer to play iTunes/Music purchases. It may help to download a free app.
Then try logging in in Podcasts Connect. There are ongoing problems at Podcasts Connect which are causing some people to have the problem you describe. Apple are aware and are working on it. There isn't really anything you can do about it except keep trying.
If you still have problems, report it to Podcasts Support. Go to https://itunespartner.apple.com/contact/?content_type=podcasts and click the 'Contact Us' link at the bottom of the page.
Occasionally people with this problem have been unable to get through to that contact page. If so, contact Support. Don't report it as a podcasting problem - they don't handle those - but as an inability to get to the contact page. It's also been suggested that getting them to look at your Apple ID may clear matters.