diff --git a/packages/auth/src/interaction/routes.test.ts b/packages/auth/src/interaction/routes.test.ts
index 50137533fe..8b5a539cb4 100644
--- a/packages/auth/src/interaction/routes.test.ts
+++ b/packages/auth/src/interaction/routes.test.ts
@@ -529,6 +529,7 @@ describe('Interaction Routes', (): void => {
     describe('IDP - Grant details', (): void => {
       let grant: Grant
       let access: Access
+      let interaction: Interaction
 
       beforeAll(async (): Promise<void> => {
         grant = await Grant.query().insert({
@@ -539,6 +540,10 @@ describe('Interaction Routes', (): void => {
           ...BASE_GRANT_ACCESS,
           grantId: grant.id
         })
+
+        interaction = await Interaction.query().insert(
+          generateBaseInteraction(grant)
+        )
       })
 
       test('Can get grant details', async (): Promise<void> => {
@@ -558,6 +563,7 @@ describe('Interaction Routes', (): void => {
         await expect(interactionRoutes.details(ctx)).resolves.toBeUndefined()
         expect(ctx.status).toBe(200)
         expect(ctx.body).toEqual({
+          grantId: grant.id,
           access: [
             {
               actions: access.actions,
diff --git a/packages/auth/src/interaction/routes.ts b/packages/auth/src/interaction/routes.ts
index 8f29ea9fa5..cb8ecf0148 100644
--- a/packages/auth/src/interaction/routes.ts
+++ b/packages/auth/src/interaction/routes.ts
@@ -146,6 +146,7 @@ async function getGrantDetails(
   )
 
   ctx.body = {
+    grantId: interaction.grant.id,
     access: access.map(toOpenPaymentsAccess),
     state: interaction.state
   }
diff --git a/packages/auth/src/openapi/specs/id-provider.yaml b/packages/auth/src/openapi/specs/id-provider.yaml
index d3be9e897b..ad5e1afd7f 100644
--- a/packages/auth/src/openapi/specs/id-provider.yaml
+++ b/packages/auth/src/openapi/specs/id-provider.yaml
@@ -129,6 +129,9 @@ paths:
                       - PENDING
                       - APPROVED
                       - DENIED
+                  grantId:
+                    description: Id of a grant
+                    type: string
         '401':
           description: Unauthorized
         '404':