Invalid signature for signature method HMAC-SHA1

Hi,

I am trying to access the User access token and secret. 

I have followed the exact same steps as mentioned in the Garmin Connect Developer Tool for User Authorization. 

In

Step 1: We have acquired the Request Token and Secret

Step 2: Authorization of Request Token and we received the oauth_verifier 

Step 3: When we try to get the user access token, I am getting an error 

HTTP Status 401 – Unauthorized

Type Status Report

Message: Invalid signature for signature method HMAC-SHA1

Description: The request has not been applied because it lacks valid authentication credentials for the target resource.

I verified the information that I am passing to generate the Signature and it seems correct.

Could you please help me to resolve the issue?

When I am generating the user access token from the Garmin Developer console it is working absolutely fine. The only difference that I found is the HMAC-SHA1 key. 

When I check this it is the combination of Consumer Secret and Request Token Secret, concatenated with &.

What is the HMAC-SHA1 key and where should I use it?

Kindly help me with this I have spent almost 2 days resolving this issue.