Hello Raúl

Amelia doesn't have any registration options, so your customers can receive a link to create a password and log into Amelia's Front-end Customer Panel only when they book an appointment. That customer, which is created doesn't need to have a WordPress user assigned, so they don't have access to back-end. You can enable that in Amelia Settings/Roles Settings/Customer, by enabling "Automatically create Amelia Customer User", but in that case, WordPress will send them another (automated) email with which they can create a password for back-end access.

So, if you only wish your customers to have access to their front-end panel, you can disable that, and let them book an appointment. After they do, if you've configured the Customer Panel properly (as explained in the documentation linked above), and added the %customer_panel_url% placeholder in the "Appointment Approved" and/or "Appointment Pending" email notification, they will receive a URL token with which they'll create a password they can later use to log into the panel.

Hello again Raúl

This is not coming from one email, is it?

The first one seems to be a token for setting up a WordPress password: https://www.agenda.efica.org.ar/wp-login.php?action=lostpassword&error=invalidkey, and the second one is for https://www.agenda.efica.org.ar/cliente-registro/ page.

If you enabled "Automatically create Amelia Customer user" in Amelia Settings/Roles Settings/Customer, the first email is generated by WordPress, which creates a WP user for every new customer. You can disable that if you don't want your customers to log into WordPress.

The %customer_panel_url% placeholder can be used as a hyperlink, so you can select a text and click on the LINK icon in the top section of the email notification; and then paste the placeholder instead of the link: