Unable to use testnet and devnet Solana endpoints to create a connection

[Danilo-Araujo-Silva]

Why we cannot use testnet and devnet endpoint defined here on the Solana documentation in order to create our connections?

Solana documentation:
https://docs.solana.com/cluster/rpc-endpoints

Testnet
https://api.testnet.solana.com

Devnet
https://api.devnet.solana.com

Using them it seems we cannot load the markets (await Market.load(connection, marketAddress, {}, programAddress)) and because of that we cannot place, cancel, or retrieve the orders.

[GiveMeSomething]

Please check that the marketAddress and programAddress actually existed on testnet/devnet.

Check the marketAddress and programAddress here

Also I think testnet don't have Serum running, but devnet does. Here is its address on devnet: DESVgJVGajEgKGXhb6XmqDHGz3VjdgP7rEVESBgxmroY

References: Serum DEX