US online retailer Wish has been reprimanded for promoting "overtly sexual" adverts within apps that should have been suitable for children.
It included an advert for a sex toy and one showing a woman wearing nipple tassels.
UK watchdog the Advertising Standards Authority (ASA) said that Wish.com must ensure that their advertisements are "appropriately targeted".
Wish did not agree that the adverts could cause "widespread offence".
In 2018, Wish.com breached similar guidelines three times in five months.
The latest rulings involved four adverts that appeared in April and May 2020.
One of the ads featured inside the BBC's Good Food Guide app.
It showed a woman from the neck down wearing a corset with her chest partially exposed, covered only by nipple tassels.
Three further advertisements, including one that featured an image of a male sex toy accompanied by descriptive language, were seen in the Google Play and Google News apps.
"We considered consumers using apps for recipes, the news and playing solitaire would not expect to see sexually explicit content," the ASA said in its ruling.
"We therefore concluded that in those contexts the ads were likely to cause both serious and widespread offence."
Wish agreed that the ads might not have been appropriate for all forums but did not agree that they were likely to cause serious or widespread offence.
Immediate Media, the creators of the BBC Good Food app, said the advert in question was delivered as a result of programmatic advertising - the automated buying and selling of online adverts.
The company did not consider the ad to be suitable for the app's audience.
The ASA has limited powers to punish offenders, but it told the BBC it can hand out a number of sanctions to deter repeat offending.
"We can place our own ads in Google searches, stating that a particular advertiser has broken the rules," said the spokesman.
The authority can also invoke mandatory pre-vetting for advertisers who have broken rules on grounds of taste and decency.
"An advertiser’s reputation can be badly damaged if it is seen to be ignoring rules designed to protect consumers," added the spokesman.
The ASA did not explain in its ruling why, given Wish's previous breaches, it had chosen a reprimand rather than one of the other sanctions.
It does not have the power to impose fines.