Problem:

When creating a Connection to my Salesforce Production or Sandbox Org, I get an OAuth error stating “We can't authorize you because of an OAuth error”. 
In many cases, the url of that error ends with …/RemoteAccess/Error/Page.apexp?error=invalid_client&error_description=app+must+be+installed+into+org .

Answer: 

Salesforce has changed the way external apps can connect to Orgs. From now on, apps need to be installed in the Org first before you can create a connection.

Installing external Plauti apps and features into your Org can be done by using an install link, or (for repeat connections only) by installing via Salesforce Setup.

This needs to be done for each Org you want to connect with and where you get the OAuth error, so both Production and related Sandboxes. Note that Sandboxes receive a new Org ID when they are refreshed, so you will need to repeat the following steps after a Sandbox refresh.

For First-time Connections

• If you have not connected the Plauti app or feature to a certain Org before, proceed here. 

The Plauti app or feature you are trying to connect to your Org needs to be installed first. 

1. Make sure you are logged in to Salesforce as a System Administrator.
2. Find the app or feature you want to connect in the list below.
3. Copy the listed link, paste it after your Org's base URL and hit Enter.
   For example, the full install link for Plauti Desktop would look similar to:
   https://my-domain.my.salesforce.com/identity/app/AppInstallApprovalPage.apexp?app_id=0CiIV0000000OK5&app_org_id=00D30000001FpeS
4. In the confirmation pop-up, click Install.
5. Confirm that the app is now listed in Salesforce Setup > (Manage) Connected Apps.
6. For some apps you will need to apply multiple links. Make sure to apply all links that are listed for the app!
   Repeat the steps above for each listed link.

• If you get an error stating “Managed Application Installation Error - You are not authorized to install managed applications.”, ask your System Administrator to install the app.

Plauti App Install Links

For Return Connections

• If you have connected the Plauti app or feature to a certain Org before, you can either use the install links as described above, or install via Salesforce Setup.

Plauti Server needs to be installed into your Salesforce Org first. If you do not see the apps in the list, use the method for First-time Connections above instead.

1. Make sure you are logged in to Salesforce as a System Administrator.
2. Go to Salesforce Setup > Apps > Connected Apps > Connected Apps OAuth Usage.
3. At the line of your connected app, click Install.
4. When asked to confirm the installation of the connected app, click Install again.
5. If your app is listed on multiple lines, e.g. ‘Plauti Server - Connect’ and ‘Plauti Server - Login’, make sure to click Install on all lines.

• If you do not see the apps in the list, use the method for First-time Connections instead.
• If you get an error stating “Managed Application Installation Error - You are not authorized to install managed applications.”, ask your System Administrator to install the app.

If you encounter any problems, or the above steps do not solve your problem, don't hesitate to contact Plauti Support.