AWS SDK SERVER 5.0.3 issues and Gamelift questions

Hello, I'm trying to use Gamelift to host our game servers (built on UE5). No problem to compile the game server using sdk/plugin and everything looks ok.

I'm trying to follow the good "AWS for game" YT series and adapt it to the new versions. No easy task sometime. I upload the build and create a fleet. Everything looks ok

Then I try the game-create-session command and I got that error:

So I want to get an RDP access to Windows on the EC2 instances for debuging:

So I try the new command

aws gamelift get-compute-access --fleet-id fleet-XXXX 

but it complains asking for a --compute-name following this regex [a-zA-Z0-9-]+|^arn:.*:compute/[a-zA-Z0-9-]+ format

I have no idea how to get the compute-name of an EC2 instance created from gamelift. The Gamelift EC2 instances are not showed in my EC2 console.

Also randomly when I try to get the instances running I got an empty array.

I'm really lost here and I can't find good ressources on these issues

[Update] Some other infos that could help to solve my issues:

Thanks!