Uniswap Trading API (Sepolia) - Intermittent 502/404 Errors on ERC20 Swaps

[am9p]

Hi everyone,

I'm encountering persistent issues with the Uniswap Trading API (https://trading-api-labs.interface.gateway.uniswap.org/v1/swap) when attempting ERC20 token swaps (e.g., WETH -> USDC) on the Sepolia testnet. I previously posted about this in the discussions forum (#7862) without a resolution, so I'm hoping someone here can help me out.

Problem:

The API https://trading-api-labs.interface.gateway.uniswap.org/v1/swapis frequently returning HTTP errors. These API errors are completely blocking the swap process, preventing transactions from being completed.

• 502 Bad Gateway
• 404 Not Found

Details:

The errors occur during the SwapTransactionAsync step within a classicSwap execution. (See screenshots below)

I'm unable to locate the source code for this specific API service to investigate further.

The swap process becomes stuck and cannot proceed due to these API errors.

Request:

Could anyone provide guidance on:

• The location of the Uniswap Trading API's source code?
• Potential causes for these intermittent 502/404 errors on the Sepolia testnet?
• Any recommended workarounds or alternative approaches for performing ERC20 swaps on Sepolia?

Thanks in advance for any help!

[plondon]

404s usually mean an issue simulating the tx, can you provide the error details in the response?

[am9p]

404s usually mean an issue simulating the tx, can you provide the error details in the response?

Thank you. Here is cURLs I saved, hope they will help:

404 Response:

curl 'https://trading-api-labs.interface.gateway.uniswap.org/v1/swap' \
  -H 'accept: */*' \
  -H 'accept-language: en-US,en;q=0.9' \
  -H 'content-type: application/json' \
  -H 'origin: https://app.uniswap.org/' \
  -H 'priority: u=1, i' \
  -H 'referer: https://app.uniswap.org/' \
  -H 'sec-ch-ua: "Not(A:Brand";v="99", "Google Chrome";v="133", "Chromium";v="133"' \
  -H 'sec-ch-ua-mobile: ?0' \
  -H 'sec-ch-ua-platform: "macOS"' \
  -H 'sec-fetch-dest: empty' \
  -H 'sec-fetch-mode: cors' \
  -H 'sec-fetch-site: same-site' \
  -H 'user-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/[133.0.0.0](http://133.0.0.0/) Safari/537.36' \
  -H 'x-api-key: JoyCGj29tT4pymvhaGciK4r1aIPvqW6W53xT1fwo' \
  -H 'x-app-version;' \
  -H 'x-request-source: uniswap-web' \
  -H 'x-universal-router-version: 2.0' \
  --data-raw '{"quote":{"chainId":11155111,"input":{"amount":"1000000000000000","token":"0xfFf9976782d46CC05630D1f6eBAb18b2324d6B14"},"output":{"amount":"24714401","token":"0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238","recipient":"0x6De6069281868f89b6A32A0003ce1da859AcB421"},"swapper":"0x6De6069281868f89b6A32A0003ce1da859AcB421","route":[[{"type":"v3-pool","address":"0x6418EEC70f50913ff0d756B48d32Ce7C02b47C47","tokenIn":{"chainId":11155111,"decimals":"18","address":"0xfFf9976782d46CC05630D1f6eBAb18b2324d6B14","symbol":"WETH"},"tokenOut":{"chainId":11155111,"decimals":"6","address":"0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238","symbol":"USDC"},"fee":"10000","liquidity":"26612353443116297","sqrtRatioX96":"501442176176779195057858884147814","tickCurrent":"175066","amountIn":"1000000000000000","amountOut":"24652614"}]],"slippage":0.5,"tradeType":"EXACT_INPUT","quoteId":"8b3098e5-d37b-46c3-8ce2-862dfe3b551a","gasFeeUSD":"0.000202359956409039","gasFeeQuote":"25743","gasUseEstimate":"240370","priceImpact":1,"txFailureReasons":[],"maxPriorityFeePerGas":"2000000000","maxFeePerGas":"2003725178","gasFee":"481635421035860","gasEstimates":[{"type":"eip1559","strategy":{"limitInflationFactor":1.15,"priceInflationFactor":1.5,"percentileThresholdFor1559Fee":75,"minPriorityFeeGwei":2,"maxPriorityFeeGwei":9},"gasLimit":"276425","gasFee":"553879732328650","maxFeePerGas":"2003725178","maxPriorityFeePerGas":"2000000000"}],"routeString":"[V3] 100.00% = WETH -- 1% [0x6418EEC70f50913ff0d756B48d32Ce7C02b47C47]USDC","blockNumber":"7904995","aggregatedOutputs":[{"amount":"24652615","token":"0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238","recipient":"0x6De6069281868f89b6A32A0003ce1da859AcB421","bps":9975,"minAmount":"24652615"},{"amount":"61786","token":"0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238","recipient":"0xE49ACc3B16c097ec88Dc9352CE4Cd57aB7e35B95","bps":25,"minAmount":"61786"}],"portionAmount":"61786","portionBips":25,"portionRecipient":"0xE49ACc3B16c097ec88Dc9352CE4Cd57aB7e35B95"},"permitData":{"domain":{"name":"Permit2","chainId":11155111,"verifyingContract":"0x000000000022D473030F116dDEE9F6B43aC78BA3"},"types":{"PermitSingle":[{"name":"details","type":"PermitDetails"},{"name":"spender","type":"address"},{"name":"sigDeadline","type":"uint256"}],"PermitDetails":[{"name":"token","type":"address"},{"name":"amount","type":"uint160"},{"name":"expiration","type":"uint48"},{"name":"nonce","type":"uint48"}]},"values":{"details":{"token":"0xfFf9976782d46CC05630D1f6eBAb18b2324d6B14","amount":"1461501637330902918203684832716283019655932542975","expiration":"1744603892","nonce":"0"},"spender":"0x3a9d48ab9751398bbfa63ad67599bb04e4bdf98b","sigDeadline":"1742013692"}},"signature":"0x162485941ba1faf21013656dab1e60e9d7226dc00000004200937eb426e63d36b6f90eed12e1e51221c0dfdaff45157529f2c21e16ed4edfc147d5d2542832f0a7ffb982af88adb737f1e22e9d12ec5101ee268df130d36d2a1b","simulateTransaction":true,"refreshGasPrice":true,"gasStrategies":[{"limitInflationFactor":1.15,"displayLimitInflationFactor":1.15,"priceInflationFactor":1.5,"percentileThresholdFor1559Fee":75,"minPriorityFeeGwei":2,"maxPriorityFeeGwei":9}],"urgency":"normal"}'

502 Response:

curl 'https://trading-api-labs.interface.gateway.uniswap.org/v1/swap' \
  -H 'accept: */*' \
  -H 'accept-language: en-US,en;q=0.9' \
  -H 'content-type: application/json' \
  -H 'origin: https://app.uniswap.org/' \
  -H 'priority: u=1, i' \
  -H 'referer: https://app.uniswap.org/' \
  -H 'sec-ch-ua: "Not(A:Brand";v="99", "Google Chrome";v="133", "Chromium";v="133"' \
  -H 'sec-ch-ua-mobile: ?0' \
  -H 'sec-ch-ua-platform: "macOS"' \
  -H 'sec-fetch-dest: empty' \
  -H 'sec-fetch-mode: cors' \
  -H 'sec-fetch-site: same-site' \
  -H 'user-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/[133.0.0.0](http://133.0.0.0/) Safari/537.36' \
  -H 'x-api-key: JoyCGj29tT4pymvhaGciK4r1aIPvqW6W53xT1fwo' \
  -H 'x-app-version;' \
  -H 'x-request-source: uniswap-web' \
  -H 'x-universal-router-version: 2.0' \
  --data-raw '{"quote":{"chainId":11155111,"input":{"amount":"1000000000000000","token":"0xfFf9976782d46CC05630D1f6eBAb18b2324d6B14"},"output":{"amount":"24714401","token":"0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238","recipient":"0x6De6069281868f89b6A32A0003ce1da859AcB421"},"swapper":"0x6De6069281868f89b6A32A0003ce1da859AcB421","route":[[{"type":"v3-pool","address":"0x6418EEC70f50913ff0d756B48d32Ce7C02b47C47","tokenIn":{"chainId":11155111,"decimals":"18","address":"0xfFf9976782d46CC05630D1f6eBAb18b2324d6B14","symbol":"WETH"},"tokenOut":{"chainId":11155111,"decimals":"6","address":"0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238","symbol":"USDC"},"fee":"10000","liquidity":"26612353443116297","sqrtRatioX96":"501442176176779195057858884147814","tickCurrent":"175066","amountIn":"1000000000000000","amountOut":"24652614"}]],"slippage":0.5,"tradeType":"EXACT_INPUT","quoteId":"41e4869f-2c52-4551-b311-f667db82fc40","gasFeeUSD":"0.00027005851867116","gasFeeQuote":"34356","gasUseEstimate":"240370","priceImpact":1,"txFailureReasons":[],"maxPriorityFeePerGas":"2000000000","maxFeePerGas":"2005547905","gasFee":"482073549924850","gasEstimates":[{"type":"eip1559","strategy":{"limitInflationFactor":1.15,"priceInflationFactor":1.5,"percentileThresholdFor1559Fee":75,"minPriorityFeeGwei":2,"maxPriorityFeeGwei":9},"gasLimit":"276425","gasFee":"554383579639625","maxFeePerGas":"2005547905","maxPriorityFeePerGas":"2000000000"}],"routeString":"[V3] 100.00% = WETH -- 1% [0x6418EEC70f50913ff0d756B48d32Ce7C02b47C47]USDC","blockNumber":"7905047","aggregatedOutputs":[{"amount":"24652615","token":"0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238","recipient":"0x6De6069281868f89b6A32A0003ce1da859AcB421","bps":9975,"minAmount":"24652615"},{"amount":"61786","token":"0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238","recipient":"0xE49ACc3B16c097ec88Dc9352CE4Cd57aB7e35B95","bps":25,"minAmount":"61786"}],"portionAmount":"61786","portionBips":25,"portionRecipient":"0xE49ACc3B16c097ec88Dc9352CE4Cd57aB7e35B95"},"permitData":{"domain":{"name":"Permit2","chainId":11155111,"verifyingContract":"0x000000000022D473030F116dDEE9F6B43aC78BA3"},"types":{"PermitSingle":[{"name":"details","type":"PermitDetails"},{"name":"spender","type":"address"},{"name":"sigDeadline","type":"uint256"}],"PermitDetails":[{"name":"token","type":"address"},{"name":"amount","type":"uint160"},{"name":"expiration","type":"uint48"},{"name":"nonce","type":"uint48"}]},"values":{"details":{"token":"0xfFf9976782d46CC05630D1f6eBAb18b2324d6B14","amount":"1461501637330902918203684832716283019655932542975","expiration":"1744604570","nonce":"0"},"spender":"0x3a9d48ab9751398bbfa63ad67599bb04e4bdf98b","sigDeadline":"1742014370"}},"signature":"0x162485941ba1faf21013656dab1e60e9d7226dc00000004200199e296ce7bc7e14b975e80af9ad99af8d052b3682734d9fce70b1507759acd425358d62cfbd4fd1a4bc288ee9d599772473dc933f517fb95be91194e44142dd1c","simulateTransaction":true,"refreshGasPrice":true,"gasStrategies":[{"limitInflationFactor":1.15,"displayLimitInflationFactor":1.15,"priceInflationFactor":1.5,"percentileThresholdFor1559Fee":75,"minPriorityFeeGwei":2,"maxPriorityFeeGwei":9}],"urgency":"normal"}'