Bubble's built-in Pinterest plugin uses an older version of Pinterest's API, which is no longer fully compatible. When you attempt to set up an OAuth connection through the plugin, the connection to Pinterest's endpoint fails.
What you might notice
An error code 11 appears when attempting to authenticate with Pinterest through Bubble's plugin
The OAuth flow doesn't complete successfully
Workaround
Use the API Connector to connect to Pinterest directly instead of Bubble's built-in plugin. The API Connector lets you set up a connection to Pinterest's current API version, giving you a more reliable and up-to-date integration.