Enabling Nintex Workflow Feature Failed - Sorry, Something Went Wrong

Finally I was bring SharePoint 2019 Up and running on On Prem. Then I wanted to test my Nintex Workflows and tried to Enable the Nintex Workflow Feature on the Site Collection Level. Then... This Happen

The Error message which we all are familiar

Sorry, something went wrong

An unexpected error has occurred.

Technical Details

Troubleshoot issues with Microsoft SharePoint Foundation.

Correlation ID: Correlation ID

Date and Time: date and time

then I followed the old fashion ULS Logs check with my ULS Viewer 

Finally Found the Culprit 

Feature receiver assembly 'Nintex.Workflow.Features, Version=1.0.0.0, Culture=neutral, PublicKeyToken=913f6bae0ca5ae12', class 'Nintex.Workflow.Features.ContentTypeUpgradeFeatureEventHandler', method 'FeatureActivated' for feature '86c83d16-605d-41b4-bfdd-c75947899ac7' threw an exception: Nintex.Workflow.NWFeatureActivatingException: Nintex.Workflow.NWDatabaseConnectionException: Failed to open a connection to the Nintex Workflow configuration database. ---> System.Data.SqlClient.SqlException: Cannot open database " Nintex workflow configuration db" requested by the login. The login failed.  Login failed for user “Domain\webapppoolAccount”.   

 at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, UInt32 waitForMultipleObjectsTimeout, Boolean allowCreate, Boolean onlyOneCheckConnection, DbConnectionOptions userOptions, DbConnectionInternal& connection)   

 at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection)   

 at System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection)   

 at System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)   

 at System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry)   

 at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)   

 at System.Data.SqlClient.SqlConnection.Open()   

 at Nintex.Workflow.Administration.Database.OpenConnectionInternal(String connectionString)   

 at Nintex.Workflow.Administration.ConfigurationDatabase.OpenConfigDataBase()     -

-- End of inner exception stack trace ---   

 at Nintex.Workflow.Administration.ConfigurationDatabase.OpenConfigDataBase()   

 at Nintex.Workflow.Administration.Database.ExecuteReader(SqlCommand command, CommandBehavior behavior)   

 at Nintex.Workflow.Administration.GlobalConfig.LoadData()   

 at Nintex.Workflow.Administration.GlobalConfig.GetGlobalConfig(Boolean forceRefresh)   

 at Nintex.Workflow.Administration.ConfigSettings.GetConfigSettings(SPSite site)   

 at Nintex.Workflow.Common.NWSharePointObjects.<>c__DisplayClass2.<SetMultiOutcomeTaskEditForm>b__0()   

 at Microsoft.SharePoint.Utilities.SecurityContext.RunAsProcess(CodeToRunElevated secureCode)   

 at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(WaitCallback secureCode, Object param)   

 at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(CodeToRunElevated secureCode)   

 at Nintex.Workflow.Common.NWSharePointObjects.SetMultiOutcomeTaskEditForm(SPWeb web)   

 at Nintex.Workflow.Features.ContentTypeUpgradeFeatureEventHandler.FeatureActivated(SPFeatureReceiverProperties props)   

 at Nintex.Workflow.Features.ContentTypeUpgradeFeatureEventHandler.FeatureActivated(SPFeatureReceiverProperties props)   

 at Microsoft.SharePoint.SPFeature.DoActivationCallout(Boolean fActivate, Boolean fForce)

Simply issue was In the Database Server, Nintex Workflow Configuration Database does not have enough permission for the Web Application App Pool Account. 

Resolution

then I gave the same permission as Contant Database which is WSS_Content_Application_Pools Permission on DB Account Permission Section 

Then once permission provided, I was able to successfully enable the required Nintex Workflow Features 

hope This might help someone like me :) Leave me a comment in case if it was helpful.