error: You provided 'undefined' where a stream is expected. You can provide an Observable, Promise, ReadableStream, Array, Asynciterable, or Iterable.

When you press Search for new FC another error shows (below image): Error getting LWA Access Token on Marketplace

When you check your marketplace settings, the API is connected.

Solution:

To resolve this, you need to re-authorize SMP. Please visit your Amazon Seller Central and go to "Manage my Apps" which should bring you to the necessary page referenced in the screenshot below. Once your account is re-authorized, it will redirect you to sign back into your SMP account.