Unable to find nuget package locally - gitlab-ci.yml for dotnet core

I am trying to build dotnet project using .gitlab-ci.yml. Everything was fine until I had to use custom Nuget package. I dont have enough background on .net and based on quick read from documentation I found that I can use something like dotnet build --source c:\packages\mypackages so I used the script below. But I keep getting error

/builds/xxx/xx/xx/Status.csproj : error NU1101: Unable to find package LDAPLoginAuthentication. No packages exist with this id in source(s): nuget.org [/builds/xx/xx/Status.sln]

mage : mcr.microsoft.com/dotnet/core/sdk:3.1

variables:
  NUGET_PACKAGE: /nugets-package

stages:
  - build

build:
  stage: build
  only:
    - development
  script:
    - echo "I am building"
    - dotnet build --source "$NUGET_PACKAGE/"

Any help will be appreciated. Thanks