How To Fix /UI5/DTA021 - Mandatory URL parameter 'layer' missing or invalid

/UI5/DTA021 - Overview

• Message type: E = Error

• Message class: /UI5/DTA -

• Message number: 021

• Message text: Mandatory URL parameter 'layer' missing or invalid

Self-Explanatory Message

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To make things easier, more detailed information is frequently added to describe the issue, how to fix it, and the necessary steps or configuration modifications.

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/UI5/DTA021 - Details

• The SAP error message /UI5/DTA021 Mandatory URL parameter 'layer' missing or invalid typically occurs in the context of SAP Fiori applications or SAPUI5 applications when the application is trying to access a resource or service that requires a specific URL parameter named layer. This parameter is often used to define the layer of the application or the data being accessed, such as "base," "custom," or "test."
  
  Cause:
  
  Missing Parameter: The URL being accessed does not include the layer parameter, which is required for the application to function correctly.
  Invalid Parameter: The layer parameter is present but has an invalid value that the application does not recognize or support.
  
  Configuration Issues: There may be issues in the configuration of the application or the service that is being accessed, leading to the absence or misconfiguration of the layer parameter.
  Routing Issues: The routing configuration in the application may not be set up correctly, causing the application to