¿Por qué no ha llegado el cliente potencial al servicio si no se ha seleccionado la opción de envío sólo después del pago?

The checkbox for sending data only after payment is available in several sections of the website settings. This rule can be set at the payment system level and at the individual receiver level. 

By default, the connected payment system settings include a rule that prohibits sending orders to data capture services without payment. It is available at the bottom of the page with payment integration settings and looks like this:

This checkbox is used to disallow sending unpaid orders to connected data capture services, even if the same rule is not enabled in the receiver settings. Payment integration settings are more important than the settings of an individual data capture service.

More information about why leads are not sent to connected services:

https://answers.tilda.cc/en/a/form-submissions-not-being-received/