Halliday had been suspended by the party over allegations of inappropriate sexual conduct towards a 17-year-old girl.
He had previously told Wales Online:
"I don’t know who has made the allegation.
"I have not acted inappropriately towards anyone and am anxious to clear my name."This evening BBC News reports:
Paul Halliday claimed the Lib Dems have told him nothing about allegations leading to his suspension this month.
The former church minister said he had given evidence to fraud police that text messages were falsely sent in his name, as if they came from his phone.
The National Fraud Intelligence Bureau said it was looking into his claims.
The Lib Dems have declined to comment.Halliday announced his resignation on the Three Muckrackers vlog.