Understanding the signature base url used by postman for OAuth1.0

I am trying to call an api with OAuth 1.0 authentication. I am seeing that Postman is generating a completely different signature even though i am using the same details to hash the signature. I believe the issue is with how postman generates the signature base url. Details are below
URL: https://localhost:4567/fun
consumerkey: a
consumersecret: b
token: 123
tokensecret: abc

signature base string: GET&https%3A%2F%2Flocalhost%3A4567%2Ffun&oauth_consumer_key%3Da%26oauth_nonce%3D3%26oauth_signature_method%3DHMAC-SHA1%26oauth_timestamp%3D123%26oauth_token%3D123%26oauth_version%3D1.0

signature generated: 9GMRODNu5WWnQPMoPrJWqsT4nVI%3D

But Postman generated a completely different signature for the same details

postman signature: XAhLtCyO4m8BHcIPuCNTV4czKfM%3D

Postman Request Code:
GET /fun? HTTP/1.1
Host: localhost:4567
Authorization: OAuth oauth_consumer_key=“a”,oauth_token=“123”,oauth_signature_method=“HMAC-SHA1”,oauth_timestamp=“123”,oauth_nonce=“3”,oauth_version=“1.0”,oauth_signature=“XAhLtCyO4m8BHcIPuCNTV4czKfM%3D”

Please help me with the postman format for the signature base string?