@tonyny2016
We still provide documents for legacy Market Data APIs in the RFA 7.x package. It locates under the folder.
<RFA 7.6/7.7 install folder>/Legacy/Docs/. It's filename tmsgapi.pdf.
Note that only RDC named user can download the RFA package from
https://developers.refinitiv.com/en/api-catalog/thomson-reuters-enterprise-platform/robust-foundation-api-rfa-c--/downloads
If you still have RFA 7.6.2 package or you have permission to download RFA, you can find the document under the folder.