For small shop owners it’s a vicious cycle. They don’t want to take in Scottish notes because many customers won’t want them as change. Customers don’t want them as change because a lot of shop owners won’t take them.
As per the article, they’re not legal tender so no one is required to take them as payment.
That's not what legal tender means. Legal tender is what must be accepted in settlement of a debt. Buying something in a shop does not involve any debt and the shopkeeper can accept or not any form of payment they like including legal tender.
As per the article, they’re not legal tender so no one is required to take them as payment.