added support for older eip1271 implementations

src/helpers/eip1271.ts

@@ -29,6 +29,36 @@ const spec = {
   ],
 };
 
+// support for older eip1271 implementations
+const spec_oldVersion = {
+  magicValue: "0x20c13b0b",
+  abi: [
+    {
+      constant: true,
+      inputs: [
+        {
+          name: "_hash",
+          type: "bytes",
+        },
+        {
+          name: "_sig",
+          type: "bytes",
+        },
+      ],
+      name: "isValidSignature",
+      outputs: [
+        {
+          name: "magicValue",
+          type: "bytes4",
+        },
+      ],
+      payable: false,
+      stateMutability: "view",
+      type: "function",
+    },
+  ],
+};
+
 async function isValidSignature(
   address: string,
   sig: string,
@@ -44,6 +74,18 @@ async function isValidSignature(
       sig,
     );
   } catch (e) {
+    // if failed is latest then it might be older implementation
+    if (magicValue === eip1271.spec.magicValue) {
+      return isValidSignature(
+        address,
+        sig,
+        data,
+        provider,
+        spec_oldVersion.abi, // old spec version abi
+        spec_oldVersion.magicValue, // old spec version magicValue
+      );
+    }
+
     return false;
   }
   return returnValue.toLowerCase() === magicValue.toLowerCase();