Hey kids!! Let’s draw a picture by connecting the dots!!
The Treatise on the Success and Obstructions in the Spread of the Dharma (Fayun tongsai zhi 法運通塞志) in Zhipan’s 志磐 (ca. 1220–1275) monumental Comprehensive History of the Buddhist Patriarchs (Fozu tongji 佛祖統紀), includes the following:
扶南國沙門曼陀羅來進珊瑚佛像。詔譯經於揚都。
[In 503 AD] The śramaṇa Mandra 曼陀羅 [or Mantra?] from the kingdom of Funan 扶南 came to present a coral Buddha image. A decree was issued for him to translate scriptures in Yangdu 揚都 [i.e., Jiankang].
五年。扶南國沙門僧伽波羅來。
In the fifth year [506 AD], the śramaṇa Saṅghabhara 僧伽波羅 from the kingdom of Funan arrived.
五年。勅沙門寶雲。往扶南國迎佛髮。
[In 539] In the fifth year, an imperial decree was issued to the śramaṇa Baoyun 寶雲, instructing him to go to the country of Funan to receive [a relic of] the Buddha’s hair.
扶南國王遣使朝貢。請釋迦像及經論。勅賜。制止涅槃般若金光明講疏一百三卷。
[In 540 AD] The king of the kingdom of Funan sent envoys to pay tribute, requesting an image of Śākyamuni and copies of scriptures and treatises. By imperial command, they were granted. The emperor issued a decree bestowing annotated versions of the Nirvāṇa Sūtra, the Prajñā Sūtra, and the Golden Light Sūtra, totaling 103 scrolls.
[佛祖統紀卷第三十七 / 法運通塞志第十七之四]
The account of Zhenla in the History of the Sui (646) then states as follows:
其王姓剎利氏，名質多斯那。自其祖漸已強盛，至質多斯那，遂兼扶南而有之。
The king is surnamed Kṣatriya (Chali 剎利) and his given name is Citrasena (Zhiduosina 質多斯那). From the time of his ancestors, [the kingdom] gradually grew stronger, and by the time of Chitrasena, it annexed and took possession of Funan.
Then at the end of that century (the seventh century), Yijing 義淨 wrote in his A Record of Buddhist Practices Sent Home from the Southern Sea (Nanhai jigui neifa zhuan 南海寄歸内法傳) that,
西南一月至跋南國，舊云扶南，先是裸國，人多事天，後乃佛法盛流；惡王今並除滅，逈無僧眾，外道雜居。斯即贍部南隅，非海洲也。
Traveling one month to the southwest [of Champa], one reaches the kingdom of Banan 跋南, formerly called Funan 扶南. In earlier times, it was a naked people’s country, where most practiced the worship of heaven. Later, however, the Buddha’s teachings spread widely and flourished. A wicked king has now destroyed everything, and there are absolutely no Buddhist monks remaining. Heterodox practitioners now live mixed together. This is located in the southern corner of Jambu[dvīpa]. It is not an island in the sea.
Do you see the picture now?