Reverb employs a make/model/year/finish guesser that tries to extract well-known attributes from your product titles. Make and model are required for listing creation, but sometimes we can't guess them from your title because we don't have enough data.
To fix this, use the Custom Fields tab in your BigCommerce product page to designate the correct value for Model. Enter reverb_model in the Custom Field Name field and the corresponding name in the Custom Field Value field. See example below: