Encountered such error when connecting the sheet first time at Google Sheet:
Exception: Request failed for https://xxx.com returned code 403. Truncated server response: <!DOCTYPE HTML PUBLIC “-//IETF//DTD HTML 2.0//EN”> <html><head> <title>403 Forbidden</title> </head><body> <h1>Forbidden</h1> <p>You don’t have per… (use muteHttpExceptions option to examine full response)
Took some time to find out that it seems the .htaccess file in WordPress is preventing the access. I just changed the .htaccess to allow from all and get it fixed.