"I can't make online payments because my credit card security got rejected."
"The site has been flagged by antivirus software."
"I got held up by security."
"I got held up by ~" [「〜にひっかかった」](https://eikaiwa.dmm.com/uknow/questions/106861/)
"security" 「セキュリティ」
"I can't make online payments because my credit card security got rejected."
"I can't ~" 「〜できない」
"make online payments" 「オンライン決済」
"because ~" 「〜ので」
"my credit card security" 「クレジットカードのセキュリティ」
"got rejected" 「弾かれて」
"The site has been flagged by antivirus software."
"the site" 「そのサイト」
"has been flagged by ~" 「〜にひっかかった」
"antivirus software" 「ウィルスソフトのセキュリティ」