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How to handle contract errors

Handle errors from contracts

To understand why placing or redeeming bet transaction may be reverted, it's highly recommended to handle errors.

In most cases of operation fail, contracts return an error code (which is a hex - 4-byte error call selector of error name, for example, 0xfd25ed88 = SmallOdds from the Core contract).

You can log and handle these errors for a better UX (show to your user what exactly went wrong) and support. All errors are included in contracts ABI.

See detailed description in Contracts section.

Example of universal getter of contract error (wagmi/viem)


Please note, the error can be transmitted from different ABI for a transaction and may be nested in a sublevel of an error. E.g. "bet" in ProxyFront may return an error from ProxyFront, LP or Core (Prematch / Express).

import { decodeErrorResult, isHex } from 'viem'
import { coreABI, expressABI, freebetABI, proxyFrontABI, lpABI } from 'path/to/abi'
const abis = [ coreABI, expressABI, lpABI, freebetABI, proxyFrontABI ]
const getContractErrorHashFromError = (error: any): string | undefined => {
  if (error?.version && /viem/.test(error.version)) {
    const code = error?.data
    if (!isHex(code) && error?.cause) {
      return getContractErrorHashFromError(error.cause)
    return code
export default function getContractErrorInfo(error: any) {
  const hex = getContractErrorHashFromError(error)
  if (!isHex(hex)) {
    return {
      hex: null,
      name: null,
  let foundErrorName = null
  abis.some((abi) => {
    try {
      const { errorName } = decodeErrorResult({
        data: hex,
      foundErrorName = errorName
    catch {}
    return foundErrorName
  return {
    name: foundErrorName,