AMP doesn’t use start scripts at all, it builds the start command from the version info you select in AMP.
You’ll want to run the script on your PC and upload those files to AMP, or use the amp Linux user to run the script.
sudo su -l amp
cd .ampdata/instances/TheInstanceName01/Minecraft
./serverstart.sh
There’s a guide here that goes over most install cases:
https://discourse.cubecoders.com/t/setting-up-a-modded-java-minecraft-server/26535