Delphi XE10.1 DataSnap Client Error “SetConnectTimeOut”

You are not doing anything wrong. Embarcadero did.

In Delphi 10 Seattle (I don't have XE8), the implementation of the Data.DbxHTTPLayer.TDSHTTPNativeClient.SetConnectTimeout method is:

procedure TDSHTTPNativeClient.SetConnectTimeout(AMilisec: Integer);begin  FHTTP.ConnectTimeout := AMilisec;end;

In Delphi 10.1 Berlin, the same method looks like this:

procedure TDSHTTPNativeClient.SetConnectTimeout(AMilisec: Integer);begin  raise ENotImplemented.Create('SetConnectTimeout');end;

I edited the source (Data.DbxHTTPLayer.pas) to:

procedure TDSHTTPNativeClient.SetConnectTimeout(AMilisec: Integer);begin  FHTTPClient.ConnectionTimeout := AMilisec;  //raise ENotImplemented.Create('SetConnectTimeout');end;

And it solved the problem. The original .dcu and .o initially prevented the change from actually being linked into my app, so I added Data.DbxHTTPLayer.pas to my project (this was probably not the correct way to do it).