Make checkout errors specific and recoverable

Map each checkout validation rule to a timely, field-targeted message and a valid next action.

Skip this if Payment-decline messages or Shopify-native rules the merchant cannot change

The decision: for every material validation rule the team controls, show a field-targeted message that names the exact problem and the next valid action. Do not display it before the shopper has had a fair chance to finish the input.

A generic message such as “Invalid value” makes the shopper diagnose the rule. Baymard recommends adapting the message to the failed subrule so the correction is explicit.[1] Its separate inline-validation research warns that feedback can become distracting when it fires while the user is still entering a valid value, and that a corrected field should visibly return to a resolved state.[2] These findings support a mechanism, not a universal trigger time or conversion claim.