According to Microsoft, when using a local SQL Server non-admin or non-Windows account with their provider, if the Provider String option is used, it must also contain a User ID parameter. This article from Microsoft goes into those details: Access to the remote server is denied because no login-mapping exists. | Microsoft Learn
DBAmp Linked Servers only need a provider string if you are connecting to a sandbox, or if your Salesforce org requires a MyDomain URL to log in. In that case, if you are getting this error, your Provider String should look like: ‘App=https://test.salesforce.com;User ID=<local_Sql_Login>’ or ‘App=<your MyDomain URL>;User ID=<local_Sql_Login>’