diff --git a/cmd/wallet/balance.go b/cmd/wallet/balance.go
index 89049e1..af26eca 100644
--- a/cmd/wallet/balance.go
+++ b/cmd/wallet/balance.go
@@ -19,9 +19,34 @@ type BalancesResponse struct {
 	Balances      []ChainBalance `json:"balances"`
 }
 
+// FlexibleString holds a value the API has returned as either a JSON string
+// or a JSON number, normalising both to string.
+type FlexibleString string
+
+func (f *FlexibleString) UnmarshalJSON(b []byte) error {
+	// Per the Unmarshaler contract, null is a no-op.
+	if string(b) == "null" {
+		return nil
+	}
+	if len(b) > 0 && b[0] == '"' {
+		var s string
+		if err := json.Unmarshal(b, &s); err != nil {
+			return err
+		}
+		*f = FlexibleString(s)
+		return nil
+	}
+	var n json.Number
+	if err := json.Unmarshal(b, &n); err != nil {
+		return err
+	}
+	*f = FlexibleString(n.String())
+	return nil
+}
+
 // ChainBalance holds the balance for a single chain.
 type ChainBalance struct {
-	ChainID       string         `json:"chainId"`
+	ChainID       FlexibleString `json:"chainId"`
 	ChainName     string         `json:"chainName"`
 	NativeBalance string         `json:"nativeBalance"`
 	Tokens        []TokenBalance `json:"tokens"`
diff --git a/cmd/wallet/flexstring_test.go b/cmd/wallet/flexstring_test.go
new file mode 100644
index 0000000..feedad2
--- /dev/null
+++ b/cmd/wallet/flexstring_test.go
@@ -0,0 +1,49 @@
+package wallet_test
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/keeperhub/cli/cmd/wallet"
+)
+
+func TestFlexibleStringAcceptsBothShapes(t *testing.T) {
+	// success cases: number and string both normalise to the same string value.
+	for _, tc := range []struct{ in, want string }{
+		{`{"chainId":11155111}`, "11155111"},   // current API — returned *json.UnmarshalTypeError before this fix
+		{`{"chainId":"11155111"}`, "11155111"}, // legacy API — must keep working
+		{`{"chainId":null}`, ""},               // null is a no-op; zero value preserved
+	} {
+		var cb wallet.ChainBalance
+		if err := json.Unmarshal([]byte(tc.in), &cb); err != nil {
+			t.Fatalf("ChainBalance %s: %v", tc.in, err)
+		}
+		if string(cb.ChainID) != tc.want {
+			t.Fatalf("ChainBalance %s: got %q want %q", tc.in, cb.ChainID, tc.want)
+		}
+
+		var tok wallet.Token
+		if err := json.Unmarshal([]byte(tc.in), &tok); err != nil {
+			t.Fatalf("Token %s: %v", tc.in, err)
+		}
+		if string(tok.ChainID) != tc.want {
+			t.Fatalf("Token %s: got %q want %q", tc.in, tok.ChainID, tc.want)
+		}
+	}
+
+	// error cases: non-string, non-number JSON values must return an error.
+	for _, bad := range []string{
+		`{"chainId":{"x":1}}`,
+		`{"chainId":true}`,
+		`{"chainId":[1,2]}`,
+	} {
+		var cb wallet.ChainBalance
+		if err := json.Unmarshal([]byte(bad), &cb); err == nil {
+			t.Fatalf("ChainBalance %s: expected error, got nil", bad)
+		}
+		var tok wallet.Token
+		if err := json.Unmarshal([]byte(bad), &tok); err == nil {
+			t.Fatalf("Token %s: expected error, got nil", bad)
+		}
+	}
+}
diff --git a/cmd/wallet/tokens.go b/cmd/wallet/tokens.go
index e453d90..f7115e7 100644
--- a/cmd/wallet/tokens.go
+++ b/cmd/wallet/tokens.go
@@ -20,11 +20,11 @@ type TokensResponse struct {
 
 // Token holds metadata for a single supported token.
 type Token struct {
-	ChainID      string `json:"chainId"`
-	TokenAddress string `json:"tokenAddress"`
-	Symbol       string `json:"symbol"`
-	Name         string `json:"name"`
-	Decimals     int    `json:"decimals"`
+	ChainID      FlexibleString `json:"chainId"`
+	TokenAddress string         `json:"tokenAddress"`
+	Symbol       string         `json:"symbol"`
+	Name         string         `json:"name"`
+	Decimals     int            `json:"decimals"`
 }
 
 func NewTokensCmd(f *cmdutil.Factory) *cobra.Command {