An unexpected error occurred while inserting Opportunity records and we couldn't check your work. Make sure Opportunity records can be inserted in this org, and click "Check Challenge" again. If this continues, contact the Trailhead Help team.

Hi @Nikhitha M - Please ensure the below two things 

1. Click setup-  object manager - oppurtunity -- fields&relationsship -- close Reason -- 

edit -- Picklist (Multi-Select) Options -- deselect the checkbox Restrict picklist to the values defined in the value set.

2. First click setup then open object manager -- Select opportunity -- open field dependencies and edit field dependencies and make sure every lost and won values are included then save it then check your challenge.