RETAIN DATA IN SENSITIVE CREDIT CARD FIELDS AFTER VALIDATION ERRORS

Summary from the TLDR Design newsletter

Even though reentering credit card information frustrates users, 34% of test sites don't keep credit card numbers when errors happen. Persisting card data saves time and allows users to review potentially incorrect input and find the error. Comply with PCI standards and mitigate user frustration by validating input field-by-field, splitting the checkout flow, and validating input in two stages.