Unable to upload the documents in Form

Issue

The upload select button is unselectable with a warning: You do not have permission to access the upload file on this form. Contact the form owner or portal administrator to request the access.
Steps to reproduce:
1. Create a form with the 'upload' field.
2. Check the Allow Guest Users to Send Files under Basic.
3. Publish the form.
4. Create a content page and deploy the created form.
5. Create a User by navigating to Control Panel > Users & Organization.
6. Only give the required information (The Guest role is automatically assigned).
7. Sign out as admin and log in with guest user.
Expected Behavior: The guest user should be able to upload the document in the form.
Actual Behavior: The guest user is not able to upload the document in the form.

We need to assign the user to the same site where the form was created to use the upload field.
Follow the below steps to assign the membership to the user:
1. Click on Control Panel > Users & Organization under User.
2. Select the appropriate User.
3. Click on Memberships.
4. Select the site where the form was created.
5. Click Save.
6. Log in with the guest user.
Result: The Guest user is now able to upload the file.