For gerber file which  the bottom copper layer just has pads , the engineer will cancel or hold  the order and just want to check if the bottom layer is right or you just want to make one layer boards.

Because many customers  just want to make one layer boards but they place the wrong order layer online or some customers export the wrong bottom copper layer, so we always check this with customers.

For this issues, we have below suggestions.

If the holes and vias are plated ,then the boards should be 2 layer boards and bottom layer just have soldering pads.

If the holes or vias are non-plated ,then the boards should be one layer and bottom layer will be empty.

If the orders are canceled or held, pls contact us by email or message or online chat tooling about your suggestions ,then we will audit the order ,thanks