Did your email say "Whitney Portal" or “Lone Pine” campground?
Lone Pine campground is closed due to flooding from Spring runoff. Rec.Gov is indicating that the Lone Pine Campground will open August 1. However, this doesn't help you.
Your alternative is to camp at the Portal (a much better solution since it will be a lot cooler, and you are at elevation).
I suggest the "Ravine Campground." It's located off the overflow parking lot, near the Trailhead. There is no water or bathroom facilities at the Ravine site, however, you would get your water from next to the bathroom at the overflow lot, a slight walk from the campsite.
Yes, it is slightly inconvenient, but a great site, in the trees. Each site is developed, table, firepit and graded for a tent.
It is first come, however there are 9 or more sites to choose from....I stayed the June 26th.
Checkout the site:
https://www.fs.usda.gov/recarea/inyo/recarea/?recid=20704Paul