Shopify was hit with an outage on Cyber Monday, leaving some users and businesses unable to complete transactions during one of the biggest shopping days of the year.

In an update to its status page, the Canadian e-commerce company said select merchants were experiencing issues logging into Shopify, while others were unable to access point-of-sale systems, a critical portal used to manage transactions and other backend processes.

“We are still investigating and applying mitigations for the admin and login issues,” the company wrote on its status page around 12:20 p.m. EST.

A Shopify spokesperson pointed CNBC to its status page when reached for comment.

The Downdetector website showed thousands of users reporting problems with Shopify around 1:15 p.m. EST, after roughly 4,000 cases were reported by users at its peak at 11:00 a.m. EST.

Shopify sells software for merchants who run online businesses as well as services such as advertising and payment processing tools.

Shopify says it handles more than 10% of all e-commerce transactions in the U.S.

The company made its name as a platform for small businesses and direct-to-consumer brands, but it increasingly hosts online storefronts for larger retailers like Reebok, Mattel, Barnes & Noble and Nestle.

The outage coincided with the Cyber Monday discount bonanza, when holiday shoppers rushed to snap up discounted products.

Adobe Analytics estimates that U.S. shoppers will spend $14.2 billion online Monday, up 6.3% from a year earlier.

American shoppers spent $11.8 billion on Black Friday, marking a 9.1% jump from last year, according to Adobe.