A user's OTP credentials are generated using different OTP profiles with different USAGE TYPEs.
Restapi is able to delete only the default credential associated with the profile of the organization when deleting the credentials. User credentials other than the default ones cannot be deleted as of now.
Release : 9.1 SP3
Symantec-StrongAuth-DE558128_DE558130-HotFix is released to resolve the issue.