Retail - Can't ring up customers

Hello,

I am having an issue with Get To Work Retail Lot. I created a florist shop have lots of pretty floral arrangements, set them as "for sale," customers have come, I've talked to them, and now customers are ready to buy.

I get the notification that they are ready to make a purchase, however, I am unable to ring them up. I have a cash register on a store counter. I tried clicking on the register and on the customer sim but there is no option to ring up customers. 

 I would appreciate any help! Thank you!