Npm plugin fails to build

1

I have a snap that i wanted to upgrade from core18 to core20. So that means instead of using the nodejs plugin, I have to use the npm plugin.

While it builds fine with the nodejs plugin, it fails with the npm plugin, with this error:

> prebuild-install --tag-prefix @serialport/bindings@ || node-gyp rebuild

sh: 1: prebuild-install: Permission denied
sh: 1: node-gyp: Permission denied
npm ERR! code ELIFECYCLE
npm ERR! syscall spawn
npm ERR! file sh
npm ERR! errno ENOENT

The old snapcraft.yaml:

base: core18
grade: stable
confinement: strict

parts:
  my-part:
    plugin: nodejs
    nodejs-version: "12.18.3"
    nodejs-package-manager: yarn
    nodejs-yarn-version: "v1.22.4"

    source: .
    source-type: local

The new snapcraft.yaml:

base: core20
grade: stable
confinement: strict

parts:
  my-part:
    plugin: npm
    npm-node-version: "12.18.3"

    source: .
    source-type: local

The only matching forum post i found seemed to have it fixed for the nodejs plugin.

Any ideas?