I would get the customer to create (and own) the API endpoint that talks to their database, and we talk to that API endpoint instead. Then it is up to them to test and maintain that endpoint.
This avoids a situation where we get an email out of the blue explaining that there is a database change and we need to dedicate engineering resources to make sure it is compatible by a certain date, or even worse and more likely, an urgent email explaining that the integration has broke and we need it back running last week.
This avoids a situation where we get an email out of the blue explaining that there is a database change and we need to dedicate engineering resources to make sure it is compatible by a certain date, or even worse and more likely, an urgent email explaining that the integration has broke and we need it back running last week.