If you placed verification code, ads.txt and ad tags correctly - the ads will start to display within 24 hours.

If the ads do not appear make sure that your ads.txt, verification, and tags placed according to the instructions in your approval email. 

Most common issues related to the codes/tags being placed incorrectly.

Do not copy tags/codes from the approval email, download the files and copy from files.

Create a separate test page or pure HTML and place the codes there, this will ensure that none of other scripts/plugins do not interfere with the ads.

If the ads still not working please check if you have any caching/speed plugins (WP Rocket) that could be minifying scripts.

If you tried all of the above and the ads still not working - submit a ticket to support.