Invalid SCA token in unix

Question

I am trying to generate a JWT and sign it with node private key. Private key is in txt format.

token_header=echo -n '{"alg":"RS256","typ":"JWT"}' | base64 | sed s/\+/-/ | sed -E s/=+$// 

token_body=echo -n '{"exp": '1706896597',"iat":'1706896701',"iss":"123456-us-xxx","jti":"'123456_xxx_123'","SystemInitiated":true}' | base64 | sed s/\+/-/ | sed -E s/=+$// 

token_signature=echo -n "$token_header.$token_body" | openssl dgst -sha256 -binary -sign PrivateKey.key | openssl enc -base64 | tr -d '\n=' | tr -- '+/' '-_' 

complete_jwt_token=echo -n "$token_header.$token_body.$token_signature"

Using a curl command, to pass this "complete_jwt_token" and invoke an API request.

Result of curl:

{"error":"invalid_request","error_description":"Invalid SCA","error_uri":"http://some-uri?code=401"}

Kindly advise. Please let me know in which format private key should be.

curl command should post the request and receive a response.