I was having the same issue where it would not proceed past the captcha requiring multiple attempts and no connection to Amazon.

*What eventually worked was logging into Amazon from my computer browser. Went to security settings and turned "on" Two Step Verification using  my cell for text (I have never used Two-Step Verification for Amazon, so it has never been on.) After receiving the security code via text from Amazon, I entered the code into Amazon and chose to disable OTP (one time passcode) for my browser. After the setup was complete, I returned to the Quickbooks Self Employed, went to Labs and started the link process all over again. This time choosing the "fix" Intuit/Amazon link. Entered my Amazon login credentials once again but saw a new prompt this time. Before I could finish reading it, I received another text code. Entered that new passcode into the Intuit site and viola! At this very moment QB SE is adding my Amazon purchases with detailed purchase info. Hope this helps