Woocommerce Coupon Error

Hi there, I’m having trouble with Woocommerce coupons.

I’ve created some coupons for my business and for some reason, some of the customers are unable to use the coupon code. It is not about the case of the letter.

When the customers enter the coupon code, they get an error that says “Coupon usage limit has been reached.” when it’s their first time applying the coupon.
The setting of the coupon was unlimited ‘Usage limit per coupon’ & 1 ‘Usage limit per user’.

This doesn’t happen to all users but occasionally the same thing happens to my customers. Is there anyone know why this is happening and know how to fix this?

Please let me know. I don’t want to lose users.
Thanks.