Pro Sites turned off unpaid site access: This site is temporarily disabled until payment is received

Pro Sites is giving me trouble: My recent (some hours ago still worked) non-paid site is giving error "This site is temporarily disabled until payment is received. Please check back later."
When looking into the Account history it states: No history recorded for this site yet.
I did not turn on (at least intentiionally) Pay to blog on this, but Kimberly Lipari mentioned in an earlier solution "You are seeing this message because you have enabled the Pay to Blog feature and your blog is being blocked"

Where can I check if this is the case?

I also turned off the front page nag and only to see the login nag.

Am I correct in my understanding that it is possible to run a subdomain like this as cost free, ie no Pro Sites so called Pro level? I ask this because in the solution that Kimberly Lipari mentioned (https://premium.wpmudev.org/forums/topic/this-site-is-temporarily-disabled-until-payment-is-received-please-check-back-later#post-199981) she only states to GIVE pro status as a solution, but to my understanding the solution should be to turn off the "Pay to blog".