Websites blocking access until ads are allowed. Looking for advice.

If the website is sophisticated enough to detect the ad status and adjust its content accordingly, the available options may be limited. You can refer to the following article for a similar case: 

Advertising from official sources is generally not considered a security risk category.

I don’t think you can have definite answer here - ad networks are intermediaries, they rely ads/content sold to them by 2nd/3rd/4th parties and themselves have no idea what they push to the end users. So, today you may allow ad network and all will be fine, tomorrow the same ad network will advertise links to malware websites. Even Google the Skynet of today publishes malicious links to fake AV downloads, impersonating websites from time to time. So it may be just OK, until it’s not, all comes down to risk tolerance and management. 

Hi shelly,

One additional point is worth considering because you mentioned both DNS Filter and URL/Web Filter.

The two filtering layers need to be considered separately. FortiOS 7.6.6 documents that when both DNS Filter and Web Filter are applied to the same firewall policy, DNS filtering takes precedence. Therefore, whitelisting an advertisement domain in the Web Filter alone may not be sufficient if the same domain is being blocked by the DNS Filter.

I would first use the DNS and Web Filter logs to identify the specific advertising domain that is causing the website to fail, and then determine which filtering layer is blocking it.

For DNS filtering, FortiOS provides a Local Domain Filter where individual domains can be explicitly allowed, while the Web Filter provides its own URL-filter mechanism. Fortinet Administration Guide Documentation

Fortinet documents the DNS filtering behavior here:

DNS Filter — FortiOS 7.6.6

This approach lets you keep the Advertising category blocked globally while making a narrowly scoped exception only when a legitimate website actually depends on a particular advertising domain.

Hope this helps clarify how to maintain the advertising controls while addressing sites that depend on specific ad-serving domains.