integrating external point of sale (RICs) to manage online & brick/mortar inventory

Hi folks! My client is starting her ecommerce journey with a few select products, however she also has a brick and mortar where she sells lots of items, using a niched point of sale system called RICs. 

I'm looking to keep this process simple for her. Any ideas on how to best integrate squarespace inventory management tools with an older POS accustomed for Brick/Mortar? 

Thanks! Jenna