For most tokens on Etherium you have to use the uniswapv2 exchange with getPairAddress. However, there are a small number of tokens on uniswapv3
For those tokens - when you use the pairAddress reurned from getPairAddress - in getPairReserves - it never works.
Token : 0x763e23ab32a757caf751eb6659bff885111ac9f6
Block : 13950107
pairAddress : 0xf652ba140a5821c249d51a65a786c2f3d4461768
Call : https://deep-index.moralis.io/api/v2/0xf652ba140a5821c249d51a65a786c2f3d4461768/reserves?chain=eth
Result : 400 / “No reserves data found for pair”
However, looking at https://info.uniswap.org/#/pools/0xf652ba140a5821c249d51a65a786c2f3d4461768 clearly shows this is not the case.
This is true for many other examples.