Yes, you may transfer funds from any of your active managed portfolios to Cash+ Fixed before the funds are locked. 

However, clients are recommended to create a new Cash+ Fixed Portfolio before initiating an internal transfer from other portfolios. Cash+ Fixed has an auto-lock feature, which does not allow funding in trenches, and you may only do a lump-sum deposit once. Once funds are processed, the portfolio will get automatically locked and prepared for investment to start soon.

If you wish to add additional funds after the first deposit, you can do so by creating and funding a new Cash+ Fixed portfolio.