When setting up a private endpoint, the groupId should be case insensitive. For example, a CosmosDB private endpoint against the SQL API requires the groupId to be "Sql". If the groupId is "sql", the error message is unhelpful:

code: InternalServerError
message: An error occurred
details: []

Instead, the resource provider should be accommodate any case for the groupId. Or, as a second option, the resource provider should return a helpful error message, such as "Invalid groupId 'sql' was provided. Please see <insert docs url here> for more information." That's an error message a user can understand and provides a path to a solution.