So you can properly name it on the summons, mark the capacity notice, and reduce your chances of winding up with an unenforceable judgment or thrown-out case.
For example, you have a client suing a construction business known as "Five Cool Guys," because that's what's painted on the side of their company truck. You file a summons and complaint naming Five Cool Guys as the defendant and tell a process server to give the documents to anybody at their office.
Haphazardly naming parties like this, and serving "anybody" at offices and even homes, doesn't become an issue when a business defendant answers and settles before a proof of service gets filed, or in spite of the filed proof bearing incorrect information. But if they try denying service on such technicalities, you may have to make the corrections and serve the suit again, this time with the defendant aware that it's coming. Or, if you do win a judgment after incorrectly determining the company name or structure on court forms, you may run into problems trying to enforce it.
Is it a corporation or an LLC, or maybe a sole-proprietor? Is it owned by some other entity based out of state? Is it even structured at all? Is the name actually Five Cool Guys Construction Company or Five Cool Guys, Corp. or Five Cool Guys Construction Services LLC, or what?
People occasionally advertise and do business under the names of defunct corporations or expired fictitious business names, or no registration anywhere at all, with vague liability. You may eventually have a judgment thrown out for suing an incorrectly identified party and/or improperly serving the original summons. Or your client could wind up with an unenforceable judgment because the debtor's name doesn't match the name on any of the accounts and assets you believe they have.
In order to properly name and mark the capacity notice on a summons for a business defendant, you should find out how that business is structured and exactly how they are named in their government registrations.