I'm struggling with this error, the contract is from a famous Blockchain Dev Youtuber Hashlips and i've used it months ago without error, but now when i put it into REMIX Ide it gives me this error.

Someone could help me?

ERC721A Contract: https://github.com/hashlips-lab/nft-erc721-collection/blob/main/smart-contract/contracts/YourNftToken.sol

from solidity:
DeclarationError: Identifier not found or not unique.
  --> contracts/YourNftToken.sol:13:9:
13 |   using Strings for uint256;
   |         ^^^^^^^

1 Answer 1


The error says it cannot find where Strings is declared, I checked your repo and you are not importing that library from anywhere, to solve it just import the library Strings.

  • Tried to import Strings.sol from openzeppelin Library... now it gives this error: TypeError: Function needs to specify overridden contracts "ERC721A" and "IERC721A". --> Nuivo.sol:80:59: | 80 | function tokenURI(uint256 _tokenId) public view virtual override returns (string memory) { | ^^^^^^^^ Note: This contract: --> erc721a/contracts/ERC721A.sol:32:1: | 32 | contract ERC721A is IERC721A { | ^ (Relevant source part starts here and spans across multiple lines). Note: This contract:.... Jun 30, 2022 at 8:42

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