PUK code is typically required if you've entered your phone's PIN incorrectly 3 times and the SIM is then locked to prevent further guessing of the PIN.
Can't vouch for it but the following discussion (despite the title) on the Visible subreddit suggests the default PUK code:
https://www.reddit.com/r/Visible/comments/cawrg3/anyone_know_the_default_sim_pin_code/
I'd post the code here but I have no way to verify its accurracy. There are 2 mentioned, you'd want the one that folks say works. Try at your own risk but at worst you might need to get a new SIM from customer support.
It appears to work however, see:
https://community.visible.com/t5/Need-help/Default-SIM-pin/m-p/47802?search-action-id=14522013224&se...
Even with the PUK code you get a few attempts
