MarshalJSON is not getting called - golang

I had the following struct;

type ConditionState struct {
	Label string
	value int
}

For a graphql API I wanted to marshal this down to only the Label value. The value is for backend logic and I did not want to expose this information to the frontend; For example

var ConditionStateMint = ConditionState{Label: "MINT", value: 100}

I wanted to marshal to;

"MINT"

So I wrote a custom marshaller by overwriting the MarshalJSON method;

func (c *ConditionState) MarshalJSON() ([]byte, error) {
	return []byte(fmt.Sprintf("\"%s\"", c.Label)), nil
}

The problem I had was that this method was not getting called.

After furious debugging I found out it was because I was attaching this method to the pointer and not the value. see func (c *ConditionState) MarshalJSON.

This is because it the ConditionState was getting passed into the json unmarshal function as the value and not as a pointer. Simple remove the reference to attach the method to the value.

func (c ConditionState) MarshalJSON() ([]byte, error) {
	return []byte(fmt.Sprintf("\"%s\"", c.Label)), nil
}