Even though it is rare, it does happen and can be frustrating. Here are reasons why you could not have received commission on a successful purchase. (These are true across the board on any affiliate and commission-based platform)

Varying Reporting Times: It is normal for sales to not be fully reported within the first 24-48 hours and can take longer to reflect on your account.
Self-purchases: Depending on the brand, a self-purchase may be considered a breach of their Terms of Service.
Gift Cards and Coupon Codes: Sometimes, when a person utilizes a gift card or coupon code to complete a purchase (even using a Free Shipping code once on the site), it can override your affiliate link as the ‘source’ of the sale and cause a sale to be negated.
Outside Cookie Window: When a person clicks on a link but does not place the order until after the allowable cookie window has passed, this can cause a sale to be untracked. (Majority of our brands have a 30-day cookie window, but some have a 15-day or less cookie window)
Last Click Attribution: If a person clicks on your link, then another affiliate link or source, it works on a ‘last click attribution’ model, meaning the last link clicked on would get placed as the source for the sale.
Non-Commissionable Items: Some products or categories may not be eligible for commission, either because they’re heavily discounted, have a low profit margin, or fall under special restrictions set by the brand.
Security Issues Like Cookie Blockers and VPNs: Sales might not be properly tracked if the buyer’s device has cookie blockers or if they’re using a VPN, which can obscure the referral path causing the sale to not properly track.