the parcel nobody will sign for

The crate has just applauded him.

Every time someone nearby says "thank you", it gives a loud burst of applause. Nella discovered this when she tried being polite about the delivery.

Nella needs a signature before she can leave. Orin, the innkeeper, refuses to accept a box that keeps congratulating his customers. Neither wants to pay for sending it back.

The crate contains a small enchanted sound mechanism. It belongs to a puppet company performing in the market square. They use it for a scene with an invisible audience.

Their coat stand is waiting backstage, with Orin's delivery label tied around it. The company received the wrong parcel that morning.

The label on Nella's crate names the puppet company. It's underneath the inn's label, which was pasted over it. A loose corner gives the party something easy to notice.

If they help, they can take the crate to the market and bring back the coat stand. The puppeteer, Lio, is relieved to have the missing effect before the performance.

Nella gets her signature. Orin gets somewhere to put the coats.

You can keep the scene quick, or let the party negotiate a reward for sorting it out. A meal at the inn is enough if you want a small thank-you.

I'd let the players spot the loose label without a roll. Then give them a moment to decide what they'd do with a box that applauds on cue.

If the party walks past, Nella can handle the exchange herself. She can be back later, taking an exaggerated amount of care over her manners.

You can use this with an inn already in your game and change the names to fit. Nothing here needs to become a bigger plot.