Transfer from Maryland 529 to Able Now account question

I want to transfer the max $18000 from my sons 529 account to my sons Able Now account.  Both accounts have forms for this transfer but I'm trying to do it all electronically by taking a 529 distribution to my checking account that is linked to the 529 then transferring the same amount from my linked checking account to the Able Now account.  I can't find any IRS rules that prohibit doing the transfer this way.  Does anyone else know of any restrictions?
Thanks!