Instant of Stock cannot be written because a pointer of Quantity struct is used inside it.
type Quantity struct {
    InCarton float64 `json:"InCarton" bson:"InCarton"`
    InPallet float64 `json:"InPallet" bson:"InPallet"`
    InKg float64 `json:"InKg" bson:"InKg"`
    InCBM float64 `json:"InCBM" bson:"InCBM"`

type Stock struct {
    Batch `json:",inline" bson:",inline"`
    Quantity *Quantity `json:",inline" bson:",inline"`
    MovementHistory Movements `json:"MovementHistory" bson:"MovementHistory"`
    CostPerKg `json:"" bson:""`

Error message is described as below:

panic: cannot transform type *simcel.TransportOrderLine to a BSON Document: (struct simcel.Stock) inline fields must be either a struct or a map