I am working to implement LTI 1.3. When I am launching the LTI link, I am getting the below error:

{"errors":[{"message":"An error occurred.","error_code":"internal_server_error"}],"error_report_id":15}

undefined method `sign' for nil:NilClass

apps/canvaslms/htdocs/vendor/bundle/ruby/2.7.0/gems/json-jwt-1.13.0/lib/json/jws.rb:107:in `sign'
apps/canvaslms/htdocs/vendor/bundle/ruby/2.7.0/gems/json-jwt-1.13.0/lib/json/jws.rb:17:in `sign!'
apps/canvaslms/htdocs/vendor/bundle/ruby/2.7.0/gems/json-jwt-1.13.0/lib/json/jwt.rb:35:in `sign'
apps/canvaslms/htdocs/gems/lti-advantage/lib/lti_advantage/messages/jwt_message.rb:74:in `create_jws'