In order to use the DESelect Search in SFMC - Salesforce Marketing Cloud, users need to have the right permissions in Marketing Cloud, or they will get "401: Unauthorized" errors when performing searches.
The following user permissions are required in Marketing Cloud to be able to search for objects:

Email > Admin > API Access > WebServiceAPI

Email > Admin > API Access > WebServiceAPI
Email > Content > Email > View

Email > Interactions > Activities > Query > View

Required Permissions for DESelect Search in SFMC - Salesforce Marketing Cloud users

Security of DESelect Search in SFMC

Security

Version

DESelect

Overview

Whitelisting DESelect Segment IP

Enable DESelect Segment in new Business Units

How to configure a user to access DESelect Segment?

What are the minimum SFMC permissions to use DESelect Segment?

How to configure Schedule Selections in DESelect?

Install DESelect Segment in SFMC

Transferring user licenses

How do I install DESelect Segment in SFMC?

How do I install DESelect Segment Free?

Troubleshooting Guide: Unable to Install DESelect Search via AppExchange on Salesforce

How do I unistall DESelect Segment Free?

Installing DESelect Segment in Salesforce Marketing Cloud

Does DESelect need to create folders in Marketing Cloud?

Recommended Browser Settings

How to add the Synchronised Data Extension to my DESelect Segment account?

Why don't I have access to the Admin Panel?

DESelect Segment Free Limitations

Whitelisting DESelect Search IP

Other

Setup DESelect Segment

Does DESelect Segment offer training material?

Training Resources

Is DESelect Segment case sensitive?

What is the difference between Now and Today in Date type fields?

Is it secure to use DESelect?

What happens in DESelect when a field in a source / target data extensions is deleted?

How does DESelect Segment handle deleted Selections' Query Activities?

Which DateTime format does DESelect use?

How is the number of active users / licenses used calculated?

What types of Data Extensions does DESelect Segment support?

Are Encrypted fields supported in DESelect?

Are multibyte characters supported in DESelect?

How to optimize your Selection in DESelect Segment?

Are DESelect Segment Selections running faster / slower than Query Activities in Automation Studio?

DESelect Segment Cheat Sheet

Can I still access a Selection with a deleted Selected Data Extension?

Does Daylight Saving Time automatically apply to the time zones?

Recurring Journeys with scheduled Selections

What do you need to know to work with Data Views in SFMC?

Master Data Extensions

Cleaning up temporary Data Extensions

How do I schedule the running of my Waterfall Selection?

How can DESelect Segment help with personalization?

Can I archive my Selection?

Are Custom Data Views supported in DESelect Segment?

Can I create a Selection (ad-hoc) within my Waterfall Selection?

Can I archive my Waterfall Selection?

Which users are on the same Selection as I am?

Does "Not In" Filter exclude empty values?

When to opt for a Master DE, a Selection Template, copy the Selection, or Data Sets & Filter Sets?

Which Relation/JOIN types are supported in DESelect Segment?

What is an Extended Partnership Structure?

Why is the _Subscriber Data View not showing Results?

How to Set Up Email Integration for Error Notifications in Slack and Microsoft Teams?

Why can I not see my Data Extension in DESelect Segment?

How to Resolve "Request Failed with Status Code 500" Error?

Share your feedback with us

Can I recover/retrieve a deleted Selection?

What does DESelect store in Google Cloud?

How Can I Track Query Execution in DESelect Segment Without Automation Data Views?

How to use and manage a template

How to use DESelect Segment Data Extensions as Entry Sources in Journey Builder?

How to Use DEs Generated in DESelect Segment as an Entry Source in Journey Builder?

How to solve: "Cannot create a datafolder with a ParentFolder property of null"

How to resolve "You can only query existing data extensions or system data views" error?

How do I solve the 403 error in DESelect Segment?

Error "Violation of PRIMARY KEY constraint. Cannot insert duplicate key"

Error: 'API Permission Failed'

What affects DESelect Segment's performance?

Does DESelect Segment have a retry policy?

How to resolve _Unfiltered error?

How do I fix "Data Extension could not be updated. The SendableCustomObjectField is invalid" error when editting a Data Extension?

How to resolve “Selected Data Extension [DE Name] cannot be found. Therefore, this selection cannot be opened” error?

How to resolve “Cannot insert a NULL value into a non-nullable column” error?

How to resolve the “You do not have access” error?

How to resolve "API Permission Failed when accessing DESelect or running preview/running a Selection” error?

Why is my selection failing with a 'Automation/Query Failed due to system error,' and how can I resolve it?

How to resolve “Time-out” error?

How to resolve “Error: Query activity terminated because it has exceeded the transaction log size limit. Reducing query complexity helps prevent this error in many cases” error?

How to resolve “Error saving the Query field.'fn_' is a reserved word and may not appear in your query” error?

How to resolve "String or Binary Data Would Be Truncated" Error?

How to resolve “SOAP API” Error?

How to resolve "Retrieving Valid Relations Failed" Error?

How to solve the "ECONNREFUSED" error?

How to resolve the "Query Failed Status Code 400" error?

How to resolve the "Error saving the Query field.Invalid object name" error?

How to resolve “Data could not be retrieved, make sure Data Extension properties are provided correctly and data still exist” Error?

What are the field length limitations in DESelect?

How to Resolve “ECONNRESET” Error in DESelect?

Why is DESelect Segment loading slowly after logging in?

Troubleshooting

What is a “Selection”?

Can I copy my Selection to another Business Unit?

What is a Waterfall Selection?

Can I set my Selection as a template?

How can I modify the name my Selection?

Can I have an overview of all my scheduled Selections?

How to copy Standard or Shared Custom Values inside a Selection?

Can I create a Selection using a template?

Can I copy my Selection?

How to save folders as favorites in DESelect Segment?

How to reorder columns in the Overview page?

Step 0: Selections Overview

Can I relate Data Extensions on multiple fields?

Can I select multiple values from a Picklist?

Can Data Views be queried in DESelect Segment?

When a user changes the criteria of a selection, will DESelect modify the underlying Data Extension or will it create a new Data Extension?

How to handle timezones in filters?

Filter types in DESelect Segment

How can I use a dropdown instead of a free input field in Filters?

Is there a limit in the number of joins/rows/columns for one Selection?

How to filter on Data Extensions?

How can I use Append Data Entension?

How to work with exclusion and suppression lists?

How can you create a relationship between two Data Extensions?

Can some folders be hidden from Available Data Extensions or Target Data Extensions?

How to use Data Views with DESelect?

How to use Data Views in DESelect?

Can the user define any relationship between Data Extensions that (s)he wants?

What data can DESelect Segment use?

How does DESelect Segment work with Synchronized Data Extensions and Data Views?

How do I create my first Selection?

When to use In/Not in Results instead of adding the Data Extension to my Selected Data Extensions?

Does In/Not In filter types support Number and Decimal data types?

How to browse/ search your Data Extensions

How to quickly change the relations between my Selected Data Extensions?

Can I directly convert a date field into a different timezone in the Filters section?

Can I save and reuse a set of Filters?

Can I add Synchronized Data Extensions into DESelect Segment?

What are Behavioral Filter Sets?

Why DESelect Segment adds a "OR field IS NULL" to the SQL Query when creating DOES NOT CONTAIN filters?

Can I stop the run of a Selection that is in progress?

How can I combine 'OR' and 'AND' statements in DESelect Segment?

How to use In and Not In filter types

How to use Equals and Is not equal to filter types?

How does Contain and Does not Contain filter type works?

How does Contains one of and Does not Contain one of filter type works?

How does Begins with and Ends with filter type works?

How does Is Empty and Is not Empty filter type works?

How does Is smaller than and Is smaller than or equal to filter type works?

How does Is greater than and Is greater than or equal to filter type works?

How does Between and Not Between filter type works?

How does is after and is before filter types works?

How does in previous and in next filter types works?

How does calendar and relative filter works?

How to use In Result and Not in Result filter types?

Step 1: Selection Criteria

How can I limit and deduplicate results from multiple Data Sources within one Selection?

How to include a locale field for sending SMS?

How can I recover a deleted Custom Value?

How can I limit the results from multiple data sources/tabs within a Selection?

Date Difference Custom Value

Transform Date Custom Value

Timestamp Custom Value

Fixed Custom Value

How does the Update Data Action work in the Output Step?

How does the Append Data Action work in the Output Step?

How does the Overwrite Data Action work in the Output Step?

Can I build an Aggregation Custom Value grouping on two fields?

How does the Advanced Mode of Aggregation Custom Values work?

Can I reuse my Custom Values in any Selection?

What are the available Data Actions when configuring the output of a Selection?

What do I need to consider when editing my Target Data Extension?

Can I browse through the folders to search for the Target Data Extension that I want to use?

Row Number Custom Value

Can I combine Data Extensions that do not have any matching columns?

How to use multiple fields as the unique field in deduplication?

What field types are compatible for mappings?

Supported SQL functions

Aggregation Custom Value

How to create an Apply any function (SQL) Custom Value?

Can I do A/B testing with DESelect?

What is executed first, Sort and Limit or Deduplication?

Apply formula to a field Custom Value

What is a Custom Value?

Can I edit the fields of a Target Data Extension in DESelect Segment?

How can I deduplicate the results of my selection?

How to create a Target Data Extension on the fly in DESelect Segment?

How to map my source data to my Target Data Extension?

How does Automap work?

Dynamic Custom Value

Is there a limit on the number of Data Extensions that can be created?

How to set and populate my Target Data Extension?

What are the Data Actions available when saving data into a Data Extension in DESelect Segment?