Split Bill bug

Issue:
Split bill and payment reminders not received by recipient.
iOS 18.4
TF 6.23

Split bill last week with friend, have used multiple times before in exact same situation.
This time, bill not settled after ~ 5 days so decided (for first time) to use ‘send payment reminder’.
Again nothing after further 5 days, so text friend to find out that no initial bill split notification or indeed any follow-up reminder was received.