I accepted a request to peer review a manuscript from a journal, but was not able to view the attached files correctly and reached out to the journal three times about this problem. They finally responded and addressed the issue, but now I am less than 3 days away from their original deadline for submitting the review and I know I need at least 1-2 weeks to do an adequate job. How should I ask or state my request for more time? Is it necessary to provide the reason or justify my request for the extension in my email?
For added context, this is a journal that I'm likely to submit to in the future, so I would like to maintain an amicable relationship with the current editor.