diff --git a/packages/hoppscotch-common/src/composables/oauth2/useOAuth2GrantTypes.ts b/packages/hoppscotch-common/src/composables/oauth2/useOAuth2GrantTypes.ts
index edb650b8..f46fc923 100644
--- a/packages/hoppscotch-common/src/composables/oauth2/useOAuth2GrantTypes.ts
+++ b/packages/hoppscotch-common/src/composables/oauth2/useOAuth2GrantTypes.ts
@@ -178,6 +178,9 @@ export const useOAuth2GrantTypes = (
           id: "plain" | "S256"
           label: string
         } | null> = refWithCallbackOnChange(
+          // If the collection was imported before `codeVerifierMethod` existed,
+          // default to 'plain' when PKCE is enabled so the UI and validation
+          // remain consistent.
           auth.value.grantTypeInfo.codeVerifierMethod
             ? {
                 id: auth.value.grantTypeInfo.codeVerifierMethod,
@@ -186,7 +189,12 @@ export const useOAuth2GrantTypes = (
                     ? "Plain"
                     : "SHA-256",
               }
-            : null,
+            : auth.value.grantTypeInfo.isPKCE
+              ? {
+                  id: "plain",
+                  label: "Plain",
+                }
+              : null,
           (value) => {
             if (!("codeVerifierMethod" in auth.value.grantTypeInfo) || !value) {
               return
@@ -249,7 +257,12 @@ export const useOAuth2GrantTypes = (
             clientSecret: clientSecret.value,
             scopes: scopes.value,
             isPKCE: isPKCE.value,
-            codeVerifierMethod: codeChallenge.value?.id,
+            // Ensure older collections without `codeVerifierMethod` get a default
+            // so schema validation does not fail. Default to 'plain' when PKCE
+            // is enabled.
+            codeVerifierMethod:
+              codeChallenge.value?.id ??
+              (isPKCE.value ? ("plain" as const) : undefined),
             authRequestParams: preparedAuthRequestParams.value,
             tokenRequestParams: preparedTokenRequestParams.value,
             refreshRequestParams: preparedRefreshRequestParams.value,
diff --git a/packages/hoppscotch-common/src/helpers/import-export/import/postman.ts b/packages/hoppscotch-common/src/helpers/import-export/import/postman.ts
index b7136699..623bd539 100644
--- a/packages/hoppscotch-common/src/helpers/import-export/import/postman.ts
+++ b/packages/hoppscotch-common/src/helpers/import-export/import/postman.ts
@@ -303,6 +303,31 @@ const getHoppReqAuth = (
     const token = replacePMVarTemplating(
       getVariableValue(auth.oauth2, "accessToken") ?? ""
     )
+    const clientSecret = replacePMVarTemplating(
+      getVariableValue(auth.oauth2, "clientSecret") ?? ""
+    )
+
+    // Check for PKCE settings
+    const usePkce = getVariableValue(auth.oauth2, "usePkce")
+    const isPKCE = usePkce === "true"
+
+    // Get challenge algorithm, default to S256 if PKCE is enabled but no algorithm specified
+    const challengeAlgorithm = getVariableValue(
+      auth.oauth2,
+      "challengeAlgorithm"
+    )
+    let codeVerifierMethod: "plain" | "S256" | undefined
+
+    if (isPKCE) {
+      // Postman uses "SHA-256" or "plain" - normalize to our format
+      // Default to S256 for any value other than "plain"
+      if (challengeAlgorithm === "plain") {
+        codeVerifierMethod = "plain"
+      } else {
+        // Covers "S256", "SHA-256", undefined, and any other value
+        codeVerifierMethod = "S256"
+      }
+    }
 
     return {
       authType: "oauth-2",
@@ -314,8 +339,9 @@ const getHoppReqAuth = (
         scopes: scope,
         token: token,
         tokenEndpoint: accessTokenURL,
-        clientSecret: "",
-        isPKCE: false,
+        clientSecret: clientSecret,
+        isPKCE: isPKCE,
+        ...(codeVerifierMethod ? { codeVerifierMethod } : {}),
         authRequestParams: [],
         tokenRequestParams: [],
         refreshRequestParams: [],
diff --git a/packages/hoppscotch-common/src/services/oauth/flows/authCode.ts b/packages/hoppscotch-common/src/services/oauth/flows/authCode.ts
index 2558b0db..b3ba218d 100644
--- a/packages/hoppscotch-common/src/services/oauth/flows/authCode.ts
+++ b/packages/hoppscotch-common/src/services/oauth/flows/authCode.ts
@@ -91,11 +91,19 @@ const initAuthCodeOauthFlow = async ({
   let codeVerifier: string | undefined
   let codeChallenge: string | undefined
 
+  // Ensure backward compatibility for collections that were imported before
+  // `codeVerifierMethod` was added. If PKCE is enabled but the method is
+  // missing, default to 'plain' as requested by the user.
+  const codeVerifierMethodNormalized =
+    isPKCE && !codeVerifierMethod ? ("plain" as const) : codeVerifierMethod
+
   if (isPKCE) {
     codeVerifier = generateCodeVerifier()
+    // codeVerifierMethodNormalized might be undefined only if isPKCE is false,
+    // but here we guard with isPKCE so it's safe to pass a value.
     codeChallenge = await generateCodeChallenge(
       codeVerifier,
-      codeVerifierMethod
+      codeVerifierMethodNormalized
     )
   }
 
@@ -137,7 +145,8 @@ const initAuthCodeOauthFlow = async ({
     clientSecret,
     clientID,
     isPKCE,
-    codeVerifierMethod,
+    // Persist the normalized method so subsequent redirect handling has a value
+    codeVerifierMethod: codeVerifierMethodNormalized,
     scopes,
     authRequestParams,
     refreshRequestParams,