To maintain high quality standards, we only allow limited invites per current user.
Every member can create one invite each day. Each invite can be used two times. This means you can invite two friends each day.
How to create an invite link?
You can also follow this link
Click your avatar on the right top, then select the right tab with the user icon: 
Then click Invites and click the Create button.
Send that link to your friends.