Need Advice

I need advice with fully toilet training my almost 8 year old 😭😵 He was born 2 months early and has his fair share of issues. He was diagnosed with mild Autism when he was 4 as well as ADHD a couple years ago. This is not an excuse for him to still not be toilet trained I just wanted to add that in case anyone has a similar experience with a child on the spectrum. He's higher functioning. He knows how to use the toilet. We went to the gastro doctor a couple of times. He's super constipated but nothing medically wrong such as muscle control. He has gone about a month with no "accidents" before (minus peeing his pants while sleeping) so it's not like he can't do it. We tried sticker charts and small rewards in the past. School says he responds well to the stickers but at home he's over it after a week. He said he doesn't want to miss out on playing and I tell him he can continue to play after the bathroom. He will argue with me and sometimes teachers when it's time for a bathroom break. So I don't know if he's just being lazy about it. I want to give up but I want him to be functional in life. How do I help him with being fully trained day and night?