To create a managed package, the first step is to get the code and components from the scratch Org to the Developer Org where we have enabled the namespace. In order to do this, we need to convert the source code from the scratch format into the metadata API format.

To convert the source code into the metadata API format, run the following command in the Terminal in the directory where you have the Salesforce app. This command converts the source from the force-app, creates an API metadata equivalent, and outputs to the mdapi_output_dir directory. Notice that -n is followed by the name of the managed package application:

sfdx force:source:convert  -d mdapi_output_dir -n 'Youtube Search Application'

The following screenshot shows the components in the mdap_output_dir directory:

To deploy the code from mdapi_output_dir to the Salesforce packaging instance, we need to authenticate with the Org and then run the deploy command.

The command to authenticate with a Developer...