These are two considerations that a Salesforce admin should keep in mind when setting up the OAuth user in order to establish a secure connection with the Salesforce Maps Routing Engine. An OAuth user is required to perform optimizations for routes in Advanced Routing4. The OAuth user should have the following permissions and roles6:
The OAuth user should have the Salesforce Maps Advanced Permission Set License assigned.
The OAuth user should have the Maps Admin and SF Maps Advanced Permission Sets assigned.
The OAuth User has been assigned to a role that is above the Maps Advanced end-users in the Salesforce Role Hierarchy. The OAuth user does not need to be assigned to an active visit plan, as this is not relevant for setting up an OAuth user. The OAuth user does not need to be assigned to the 'OAuth user' profile, as this is not a valid profile in Salesforce.

Explanation
The admin should add a filter to the Lead Marker Layer used to configure Stop Associations to include only open Leads. This will ensure that stops only be associated to open Leads in the Live Daily Summaries. The filter can be added on the Marker Layer configuration page by selecting the Filters tab and choosing the appropriate criteria for open Leads. This is explained in the Configuring Stop Associations for Live Daily Summary Configurations in Salesforce Maps document.

According to the Salesforce Help document 1, this error means that the user specified in the file does not match an existing Salesforce User. The admin needs to make sure that the user name or ID in the file is correct and that the user has access to Territory Planning.

To create a data set that includes account data from Salesforce and attribute data from an external source, the customer has three options:
A) SOQL Queries: The customer can use SOQL queries to pull data from Salesforce objects and fields, and join them with external data sources, such as CSV files or web services. SOQL queries allow the customer to specify complex filters and conditions to select the relevant records and fields for the data set1. The customer can create SOQL queries in the Data Sets tab in Maps Advanced, by clicking New, selecting the object type, and choosing SOQL Query as the data source2.
C) Salesforce Reports: The customer can use Salesforce reports to create data sets that include data from multiple objects and fields, such as accounts, contacts, opportunities, and custom objects. Salesforce reports allow the customer to use report types, filters, groupings, and charts to customize the data they want to plot on the map3. The customer can create Salesforce reports in the Reports tab in Salesforce, and then use them as data sources in the Data Sets tab in Maps Advanced, by clicking New, selecting the object type, and choosing Report as the data source4.
E) External CSV: The customer can use external CSV files to import data from other systems or applications into Salesforce Maps. CSV files are comma-separated values files that store tabular data in plain text format. CSV files can include data from various sources, such as spreadsheets, databases, or web services. The customer can upload CSV files as data sources in the Data Sets tab in Maps Advanced, by clicking New, selecting the object type, and choosing CSV File as the data source5.
Reference:
1: Create Data Sets from SOQL Queries | Salesforce Help6
2: Create Data Sets | Salesforce Help7
3: Reports: The Building Blocks of Analytics | Salesforce Trailhead Module8
4: Create Data Sets from Reports | Salesforce Help9
5: Create Data Sets from CSV Files | Salesforce Help

Explanation
A visit plan can fail to populate any visits in the user's calendar for several reasons. One possible reason is that the filters and spelling are incorrect or inconsistent, which can prevent the visit plan from finding the right customers or accounts. Another possible reason is that the customers are not within the driving range of the user, which can make the visit plan unfeasible or inefficient. A third possible reason is that there are too many customers assigned to the user, which can exceed the capacity or availability of the user. These reasons are explained in the Troubleshoot Visit Plans document.