I hope they do this (so we get a default reference for all previous payees):
In the meantime, the way I deal with this is using an excellent app called Copied (I was already using it, but it’s great for this too). I’ve basically created a list in copied that has references I might need to reuse (like for paying my credit card). When I come to make a payment, I switch to the Copied keyboard, select the Payment References list, and tap on my credit card number. That way I can be sure there’s no mistyping, and it’s pretty quick and easy. Hopefully a useful workaround for you until Monzo improve the payments functionality.