Explanation
Two possible causes why no people are entering a live journey with a system generated event are:
* A wrong URL is being used. A system generated event is an event that is created and sent by an external system or application to Adobe Experience Platform using an API call. The API call must use a specific URL that contains the sandbox name, dataset id, and schema id of the event schema that defines the structure and semantics of the event data. If a wrong URL is used, such as one that contains an incorrect or missing sandbox name, dataset id, or schema id, the API call will fail and the event will not be created or sent to Adobe Experience Platform and Adobe Journey Optimizer.
* The event payload does not contain an event id. An event id is a property that uniquely identifies an event within Adobe Experience Platform and Adobe Journey Optimizer. An event id is required for an event to be processed and ingested by Adobe Experience Platform and to trigger a journey in Adobe Journey Optimizer. If the event payload does not contain an event id, it will be rejected by Adobe Experience Platform and it will not trigger a journey in Adobe Journey Optimizer. The other options are not valid or relevant causes why no people are entering a live journey with a system generated event.
The "Allow re-entrance" option is a journey property that defines whether customers can enter a journey more than once or not. This option does not affect how events are created or sent by external systems or applications. Profile attributes are properties that describe customer characteristics or behaviors, such as name, email, or purchase history. Profile attributes do not affect how events are created or sent by external systems or applications. References:
https://experienceleague.adobe.com/docs/journey-optimizer/using/journeys/create-a-journey.html?lang=en
https://experienceleague.adobe.com/docs/experience-platform/xdm/tutorials/create-event-schema-ui.html?

Explanation
A possible reason why the developer is struggling to find a message in the execution list during message monitoring is that the message has not been triggered by a journey. Message monitoring is a feature that allows the developer to monitor how messages are performing across journeys in real-time, such as how many messages are executed, sent, delivered, opened, or clicked. Message monitoring shows only messages that have been triggered by journeys that are live or paused. If a message has not been triggered by a journey, it will not appear in the execution list during message monitoring. The other options are not valid or relevant reasons why a message would not appear in the execution list during message monitoring. A message can be used in more than one journey and still appear in the execution list for each journey execution. A message can be triggered but still in pending status and still appear in the execution list with its current status.
References:https://experienceleague.adobe.com/docs/journey-optimizer/using/message-monitoring/message-mon

Explanation
To use an audience from an external source in Adobe Journey Optimizer to send a push notification, the developer can use the Non-people Identifier namespace in the platform to use an external audience. A namespace is a unique identifier that defines the source or type of an identity field, such as email or phone number. A Non-people Identifier is a namespace that defines an identity field that is not linked to a specific person, but rather to a device or session, such as cookie ID or IP address. A Non-people Identifier can be used to match profiles from an external source with profiles in Adobe Experience Platform and target them with push notifications or other actions. Cross-Device ID and Device ID are not namespaces, but types of identity fields that can be used in Adobe Journey Optimizer. A Cross-Device ID is an identity field that stores a cross-device graph identifier that links multiple devices to a single profile. A Device ID is an identity field that stores a device-specific identifier that links a device to a profile. References:
https://experienceleague.adobe.com/docs/journey-optimizer/using/get-started/data-ingestion.html?lang=en#ident

Explanation
To lay out an email from scratch, the developer should follow these steps:
* Add Structure Components to define the layout and structure of the email, such as rows, columns, or dividers. Structure Components are used to organize and align the email content and design.
* Add Content Components to fill in the content and design of the email, such as images, texts, buttons, or links. Content Components are used to create and customize the email content and design. The other options are not valid or optimal steps to lay out an email from scratch. Adding Content Components before Structure Components would not allow the developer to organize and align the email content and design properly. Adding Visibility Components is not a necessary step to lay out an email from scratch, as they are used to control thevisibility of email content based on certain conditions or criteria.
References:
https://experienceleague.adobe.com/docs/journey-optimizer/using/email-channel/design-your-email-conten

Explanation
Email Message Presets are predefined settings that apply to email messages created in Adobe Journey Optimizer. There are two types of Email Message Presets available: Marketing and Transactional. Marketing presets are used for promotional or informational emails that are sent to a large audience and require opt-in consent from the recipients. Transactional presets are used for operational or transactional emails that are sent to individual recipients and do not require opt-in consent from the recipients. SMS and Social are not types of Email Message Presets, but types of channels that can be used in Adobe Journey Optimizer.
References:https://experienceleague.adobe.com/docs/journey-optimizer/using/email-channel/email-message-pres