The front-end validation prevents zero from being entered. "Leave empty" is the way to specify no limit. (cherry picked from commit b7f2ebb5448f7992cceec899504bdd0a29058fb9)
Related issues
Bug #6872: Captive Portal per user bandwidth field no longer accepts 0.
Fix #6872 CP bandwidth 0 is no valid
The front-end validation prevents zero from being entered. "Leave empty" is the way to specify no limit.
(cherry picked from commit b7f2ebb5448f7992cceec899504bdd0a29058fb9)