Microsoft recently updated the discovery services for dynamics 365, replacing them with a new service.
If your integration has stopped working and has gone down, there is a quick work around to get you up and running again quickly.
If you update your connection string to include the following at the end of your connection string this should get you up and running quickly.
which will leave you with something like this:
If this doesn't work you may also need to update your Core Dynamics assembly/DLL
Longer term the goal is to move over to using Application Users, rather than a username/password to authenticate.
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