Checkout can not be completed because of unexpected character of the JSON data

After filling the shipping information in the first step of checkout, I click on the “Continue” button and the site stops responding. The spinning wheel appears but it is not possible to click on anything else.

It seems the cause of this issue is a “uffef” character inserted somehow in a file. See image attached to see more information obtained from the page inspector in Firefox.

How can I find the file to edit so I can remove that character?

This issue occurs in a secondary store within the same magento installation. The main store is working fine.

How to fix the «red dot» AJAX error?

I tried your solution but did not work. I cleared cache, deploy static files, etc, but still get the same error. Any ideas?

I can solve this bug for $199.

Thank you, Dmitry. I will consider your offer. In the meantime, I think you should edit your answer in the “How to fix the red dot…” question, since it doesn’t really fix it.

I think it is just because you are low-skilled.
For the next “you should” you will be banned at all.

Yes, I’m low-skilled. That’s why I look for help from high-skilled people. However, those “high-skilled” people sometimes post wrong/low quality answers like the one you provided.

OK, banned.