hello @ae-omar, currently aeternity testnet and mainnet networks are in a “divergent” state, from the Lima protocol (v4) you are required to use the compiler v4.x, while before you must use a compiler version < 4.
the current state of things is that testnet has switched to Lima protocol but mainnet has not (details here).
In this case the javascript SDK has a built in check to warn you about this incompatibility but unfortunately the message is misleading (should be Compiler 3.2.0 support only consensus protocol less then 4(Lima)
summing up, if you are on testnet you should use latest.compiler.aepps.com while on mainnet the compiler.aepps.com is the compiler you want.