Approves a pending member using an email address.
The approveByEmail() function returns a Promise that resolves to a session token
when the specified member is approved. The session token can be applied using the
wix-members-frontend applySessionToken() function
to log the member in.
A new member's status is "PENDING"
when the site's membership policy is set to manual approval.
To learn more about setting your site's membership approval policy, see
Editing Your Member Signup Settings.
Login email address of the member to approve. Must belong to an existing member.