Authorize fails with an invalid client ID error

Last updated 21 Oct 2026

The short version

You get this error when you click Authorize in Lightning Experience. The Authorize step works only in Salesforce Classic. Switch to Classic and click Authorize again.

What you see

You click Authorize on the Site Configuration tab of the Simple Signature Configure page, and you get this error:

error=invalid_client_id&error_description=client%20identifier%20invalid

In plain words, the error says: invalid_client_id, client identifier invalid.

Why it happens

Simple Signature 5.7 and later connect the signature site to your org through an External Client App. You authorize that connection with the Authorize button. That button works only in Salesforce Classic. In Lightning Experience, the same click gives this error. Simple Signature has no way to authorize in Lightning yet.

Before you start

You need a user who can switch to Salesforce Classic. That user also needs the Simple Signature (Admin) permission set and access to the Simple Signature objects.

What to do

1. Click your profile picture at the top right. Click Switch to Salesforce Classic.
2. Click Setup at the top right. In the Quick Find box, type Installed Packages. Click Installed Packages. Find Simple Signature. Click Configure. The Simple Signature Configure page opens.
3. Click the Site Configuration tab. Check that the Client Id and Client Secret boxes hold values. If they are empty, you get a different error. Follow Connect the site to Simple Signature first.
4. Click Save Settings.
5. Click Authorize. A Salesforce sign-in page opens. Sign in as a user with the Simple Signature (Admin) permission set. Allow access. The authorization date and user now show above the Authorize button. If no date shows, click Authorize again.
6. In Schedule Refresh Job Interval (Hours), type 1. Click Schedule Refresh Job. The job keeps the authorization alive.
7. When you are done, switch back to Lightning Experience.

If your org has no Salesforce Classic

Some users cannot switch to Classic. Ask another user in your org who can switch to Classic to do the steps above. If no user in your org can switch to Classic, ask Salesforce Support if they can turn Classic on for your org. You can also open a case.

How to check it worked

1. On the Site Configuration tab, the authorization date and user show above the Authorize button.
2. No error shows after you click Authorize.

If it still does not work

Open a case. To save time, include your Simple Signature version number, the exact error text, and whether you clicked Authorize in Classic. You can also read Authorize does not work for other errors on the same button.

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Related

• All Simple Signature troubleshooting
• Install the newest version of Simple Signature. TAF works on bugs in the newest version only.