Rsync / ZIP not found

I'm experiencing an issue where basic commands are not found when executing from within my shell script. Rsync and ZIP namely

#!/bin/sh

if [ $# -eq 0 ]
  then
    echo "No arguments supplied"
    exit
fi

... 
Environment variables
...

echo "Syncing files..."
rsync -rc --exclude-from="$PROJECT_PATH/.distignore" "$PROJECT_PATH/" "$DEST_PATH/" --delete --delete-excluded

echo "Generating zip file..."
cd "$BUILD_PATH" || exit
zip -q -r "${SLUG}.zip" "$SLUG/"

module.exports = {
  tagFormat: "${version}",
  branch: "master",
  plugins: [
    "@semantic-release/commit-analyzer",
    "@semantic-release/release-notes-generator",
    ["@semantic-release/npm", { 
      npmPublish: false 
    }],
    ["@semantic-release/exec", {
      "publishCmd": "chmod +x ./bin/build-zip.sh && ./bin/build-zip.sh ${nextRelease.version}"
    }],
    ["@semantic-release/github", {
      "assets": [
        {"path": "build/build.zip", "label": "Bundle"}
      ]
    }]
  ]
};

Is this perhaps a directory or permissions issue?

Reproduce the publishCmd from the semantic-release configuration and inspect ./bin/build-zip.sh in the release environment. Check whether rsync and zip are available there and whether the script's executable permissions or command lookup differ from an interactive shell. Done means identifying the failure cause and documenting a confirmed fix or prerequisite.