ISO8601 format - Amazon Web service

I am receiving the following error: 'Timestamp 2015-06-29T15%3A08%3A27Z must be in ISO8601 format' I have double checked and I believe it is in IS08601 format (then urlencoded)

When I have matched the format again the one created within http://ift.tt/1Do0Laa it seems to be the same.

Any idea?

1. Mine: 2015-06-29T15%3A08%3A27Z
2. Theirs: 2015-06-29T15%3A12%3A47Z

Thanks,

Clare