If nostr:npub1market6g3zl4mxwx5ugw56hfg0f7dy7jnnw8t380788mvdyrnwuqgep7hd is asking for a lightning address, you can copy yours from wallet view -> at the top click your wallet name -> new window will be displayed, click on the 3 points menu and click on Copy lightning address and paste it in the market.
