Sequelize .save - undefined is not a constructor - postgresql

Question

I am trying to save some data to a Postgres database using Sequelize. This is my code to connect to the database and create the model:
import Sequelize from 'sequelize'
const getModels = Connection => {
return {
User: Connection.define('users', {
id: { type: Sequelize.STRING, primaryKey: true },
refresh_token: { type: Sequelize.STRING }
})
}
}
const getInstance = () => {
const Connection = new Sequelize(
process.env.DATABASE_URL, {
dialect: 'postgres',
logging: process.env.NODE_ENV === 'production' ? false : console.log,
omitNull: true,
}
)
return getModels(Connection)
}
export default getInstance
I am trying to save the user id and refresh_token when the user logs in (authenticating using Auth0). Here is my code to do this:
const {User} = getInstance()
const user = User.build({ id: user_id, refresh_token: refresh_token })
user.save().then(() => {
console.log('save completed')
}).catch(error => {
console.log(`Something went wrong: ${error}`)
})
I am getting this error: Something went wrong: TypeError: undefined is not a constructor (evaluating 'new net.Stream()')
If I do console.log(user.id) or user.refresh_token I get the correct info back so the .build function is working. Something is wrong with the save function though. Thanks for any help in solving it - I am using a React app with Webpack (plus server-side rendering); I'm getting some warnings about dependencies from Webpack due to Sequelize as I'm using it on the front-end, not back-end. If anyone has any ideas on how to fix these, that'd be great:
[0] ./~/sequelize/lib/sequelize.js
[0] Critical dependencies:
[0] 686:60-73 the request of a dependency is an expression
[0] # ./~/sequelize/lib/sequelize.js 686:60-73
[0] ./~/sequelize/lib/dialects/mssql/connection-manager.js
[0] Critical dependencies:
[0] 18:15-71 the request of a dependency is an expression
[0] # ./~/sequelize/lib/dialects/mssql/connection-manager.js 18:15-71
[0] ./~/sequelize/lib/dialects/mysql/connection-manager.js
[0] Critical dependencies:
[0] 18:17-60 the request of a dependency is an expression
[0] # ./~/sequelize/lib/dialects/mysql/connection-manager.js 18:17-60
[0] ./~/sequelize/lib/dialects/postgres/connection-manager.js
[0] Critical dependencies:
[0] 20:14-57 the request of a dependency is an expression
[0] # ./~/sequelize/lib/dialects/postgres/connection-manager.js 20:14-57
[0] ./~/sequelize/lib/dialects/sqlite/connection-manager.js
[0] Critical dependencies:
[0] 22:15-71 the request of a dependency is an expression
[0] # ./~/sequelize/lib/dialects/sqlite/connection-manager.js 22:15-71
[0] webpack built 3215b07a25217c8e67e0 in 13519ms
Thanks!