Can I pay off a Barclays Loan Early?

If you mean you bought some Apple products from Barclays and the loan/financing is through Barclays - you are probably best off talking to Barclays. Apple was likely paid in full already and it sounds from your short description that your financing is with Barclays, not Apple.

Remember that you are not addressing Apple here but other end users gathered for mutual tech support. Financial matters are better managed by contacting Apple directly, because they will not see your question here. We cannot give you an official or binding answer.

There is contact information for finance matters at the bottom of this Apple page:

Financing and Credit - Apple