The app supposed to disappear on March 21 but it looks like it is already gone?
A customer is looking to use this, any suggestions as the would rather not pay for an app?
The BIAS app is going to be your best bet: https://apps.shopify.com/bulk-account-invite-sender
It charges you based on the number of invites that you need to send. I’ve used this for dozens of projects in the past – it works great.
I don’t believe there’s a free way to do this in bulk.