The couple has 10 days to tie the knot.
In Oklahoma, a marriage license expires in 10 days after it's issued. Shelton and Stefani have been engaged since October 2020, when he popped the question after dating for five years.
The couple recently sparked rumors that they already got married when they were snapped by paparazzi in Santa Monica, California. The No Doubt singer appeared to be rocking a sparkly wedding band next to her engagement ring.
Last month, 51-year-old Stefani celebrated an intimate bridal shower with her family. She also revealed back in April that she and 45-year-old Shelton plan to keep their nuptials low-key.
"We're keeping it very simple. Really simple," Stefani said during her appearance on Late Night With Seth Meyers. "I think the guest list will not have a lot of musicians. It'll be like my mom and my dad. It's literally going to be just family. We are looking forward to that, though."
"It's going to be fun. We're going to make it really fun, but it's not going to be a big [event]," she continued. "It's not like the queen and king are getting married or something like that."
Shelton also revealed in April the first song he and Stefani plan to dance to as husband and wife.
"It's 'If You Leave' from the Pretty In Pink soundtrack," Shelton shared on The Tonight Show Starring Jimmy Fallon. "We talked about this. We both love the song. We're both fans of the '80s, why not? Don't you think that would be a great one, though? We've literally talked about that."