iphone texts not sending to an adroid user

I have an iPhone 13 Pro, 18.1.1 software. My hubby does not have an iphone (pixel) and most of my texts are not going through to him. I will receive a delivery failed notification so will resend as sms message. Sometimes these texts go through to his email address, some end up being sent to his texts, it’s very inconsistent!

what I’ve tried

• he has an iPad and we deregistered his number on there
• deleted his contact from my phone including email address so my texts would get emailed. Created a new contact
• restarted both phones and his iPad multiple times
• turned RCS off and on and have restarted phones (both iPhone and pixel)
• I’m not a blocked contact on his phone, about half my texts go through as sms to him
• i can text other android users and he can text other iPhone users with no issues

We are at a loss of what to do! Our phones are clearly having communication issues and we cannot figure out the root cause! Any ideas would be much appreciated!!!