A method comprising: receiving, at data processing hardware of a remote system from a user device registered with an application, an application registration request inviting an unregistered user device configured to execute the application to register the unregistered user device with the application, the application registration request comprising a unique feature associated with the unregistered user device and required for registering the unregistered user device with the application; in response to receiving the application registration request, generating, by the data processing hardware, a selectable-link for registering the unregistered user device with the application, the selectable-link comprising: an application identifier identifying the application; and a verification code used to verify that the unique feature is associated with the unregistered user device; transmitting, by the data processing hardware, a first message comprising the selectable-link to the unregistered user device using the unique feature, the first message, when received by the unregistered user device, configured to cause the unregistered user device to: display the selectable-link on a graphical user interface executing on the unregistered user device; in response to receiving a selection indication indicating selection of the selectable-link displayed on the graphical user interface to: launch the application using the application identifier; populate the application with the unique feature; and transmit the verification code to the data processing hardware in response to the unregistered user device receiving confirmation to register the unregistered user device with the application; and in response to receiving the verification code from the unregistered user device, registering, by the data processing hardware, the unregistered user device with the application. receiving, at data processing hardware of a remote system from a user device registered with an application, an application registration request inviting an unregistered user device configured to execute the application to register the unregistered user device with the application, the application registration request comprising a unique feature associated with the unregistered user device and required for registering the unregistered user device with the application; in response to receiving the application registration request, generating, by the data processing hardware, a selectable-link for registering the unregistered user device with the application, the selectable-link comprising: an application identifier identifying the application; and a verification code used to verify that the unique feature is associated with the unregistered user device; an application identifier identifying the application; and a verification code used to verify that the unique feature is associated with the unregistered user device; transmitting, by the data processing hardware, a first message comprising the selectable-link to the unregistered user device using the unique feature, the first message, when received by the unregistered user device, configured to cause the unregistered user device to: display the selectable-link on a graphical user interface executing on the unregistered user device; in response to receiving a selection indication indicating selection of the selectable-link displayed on the graphical user interface to: launch the application using the application identifier; populate the application with the unique feature; and transmit the verification code to the data processing hardware in response to the unregistered user device receiving confirmation to register the unregistered user device with the application; and display the selectable-link on a graphical user interface executing on the unregistered user device; in response to receiving a selection indication indicating selection of the selectable-link displayed on the graphical user interface to: launch the application using the application identifier; populate the application with the unique feature; and transmit the verification code to the data processing hardware in response to the unregistered user device receiving confirmation to register the unregistered user device with the application; and launch the application using the application identifier; populate the application with the unique feature; and transmit the verification code to the data processing hardware in response to the unregistered user device receiving confirmation to register the unregistered user device with the application; and in response to receiving the verification code from the unregistered user device, registering, by the data processing hardware, the unregistered user device with the application.