OAuth token expired and refresh token is not set

I am working on some HTTP APIs for which I need OAuth. I am using OAuth Package. It works at first but after some time I start getting error

> Token expired and refresh token is not set.

Here is my config

userCfg := &oauth2.Config{
    ClientID:     a.ClientID,
	ClientSecret: a.ClientSecret,
	Endpoint: oauth2.Endpoint{
		TokenURL:  a.ProviderURL,
		AuthStyle: oauth2.AuthStyleInParams, // basic auth is not supported by Ping
	},
}

I see somewhere that adding Scopes: []string{"offline_access"} can resolve this issue. It takes a lot of time for me to actually add something and then deploy and test. So i just want to know if it's the correct answer or do I need to do something else.

I fixed the problem on my own, I put a check that if a received token expires error then instead of sending the error back, I request the token again else I return the error.

refreshErr := "oauth2: token expired and refresh token is not set"

// use token source to retrieve the configured token or a new token
token, err := a.tokenSource.Token()
if err != nil && strings.Contains(err.Error(), refreshErr) {
	// update the token source
	a.tokenSource, err = a.getUserToken()
	if err != nil {
		return "", err
	}

	// get the new token
	token, err = a.tokenSource.Token()
	if err != nil {
		return "", err
	}
} else if err != nil { // some other error than refresh token error
	return "", err
}

You can define the refreshErr as a constant in your code.