There are a few reasons why you may get an error when integrating TikTok lead generation with Salesforce Marketing Cloud:
Selecting anything other than TikTok Leads under App Exchange
Incorrect log in for TikTok Ads Manager
Service Timeout Error when you create a form connection
Error stating ads.tiktok.com took too long to respond.
To troubleshoot TikTok lead generation with Salesforce Marketing Cloud integration:
Ensure you are using Google Chrome.
Ensure that you don't have an ad blocker installed in your browser.
Turn off Prevent Cross-Site Tracking and Block All Cookies in your settings.
Try refreshing the page to see if the connection is created. If not, try connecting again as creating connections can take a long time.