A business customer has a check made payable to their business and an individual. The "pay to the order of" line has the business name then the individual name. There is no "and" or "or" or symbol between the business name and the individual name. Who needs to endorse the check? Do both parties need to endorse the check?

The issuer of the check may have intended otherwise, but by leaving the intent ambiguous, the issuer made the check payable to the payees in the alternative: either party may endorse and negotiate the check, IMO.