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: https://docs.microsoft.com/en-us/archive/blogs/mdegre/access-to-the-remote-server-is-denied-because-no-login-mapping-exists
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>'
