I thought I will post my answer as I recently got into a similar issue (as of September 2019). The App is free for all users in all countries.
For me, after I received a confirmation email from Apple saying that my app is ready for sale (the email did not mention any 24 hours waiting period), I could not find my App in the App Store.
The link to view the App in the App Store in the iTunes Connect (under the App Information section at the bottom page) was broken.
After reading your comments in this thread, I went to the Pricing and Availability section of the App and edited the pricing plan again to be 0 GBP and start date Today and finish date No Finish Date.
Then, I unchecked the countries the App is available on and checked them all again and hit Save.
The App became immediately available in the App store. The link in the App information section was directing me to the App Store and no longer broken.
I hope this will help anyone who is having similar issues lately (getting a confirmation email that the App is ready for sale but cannot find it in the App Store).