Hi, forgive if you’ve checked all these things already but wanted to mention it just in case…
Capital letters dont usually make any difference
Check there’s no spaces in the address
Check the email ending, some accounts end in .com and some .co.uk and I’ve had friends thinking it’s one when it’s actually the other
Check there’s no commas instead of full stops
Check your spam/junk folder, some systems have very strong filters on them.
Sorry again if you know all this but over the years I’ve encountered many issues with emails at work and home so it could be any of the above
Good luck x