  Social media platforms, including Twitter (now X), have policies in place to
maintain a safe and trustworthy advertising environment. However, the extent to
which these policies are adhered to and enforced remains a subject of interest
and concern. We present the first large-scale audit of advertising on Twitter
focusing on compliance with the platform's advertising policies, particularly
those related to political and adult content. We investigate the compliance of
advertisements on Twitter with the platform's stated policies and the impact of
recent acquisition on the advertising activity of the platform. By analyzing
34K advertisements from ~6M tweets, collected over six months, we find evidence
of widespread noncompliance with Twitter's political and adult content
advertising policies suggesting a lack of effective ad content moderation. We
also find that Elon Musk's acquisition of Twitter had a noticeable impact on
the advertising landscape, with most existing advertisers either completely
stopping their advertising activity or reducing it. Major brands decreased
their advertising on Twitter, suggesting a negative immediate effect on the
platform's advertising revenue. Our findings underscore the importance of
external audits to monitor compliance and improve transparency in online
advertising.
