HI,I'm Dr Steve
Sores between the toes can be difficult to heal because they become infected and the infection can get deep into the skin and topical antibiotics often aren't strong enough to cure the infection. You should take him to a vet for an exam and to get oral antibiotics such as cephalexin to fight the infection. There is also a spray called Vetromycin that promotes healing by increasing the oxygen supply to the sore. Continue keeping the cone on to prevent licking and keep walking on soft surfaces. I hope this has helped. If it has would youplease click the accept button so I may receive credit for my answer. Thank you and good luck. I will check later to see if you have more questions.