Hello @Ken73,
It's strange that you don't see a send message box when you click on "message history" in your reservations.
I see one as shown in the screenshot below.
I once had a reservation payment denied because my recent credit card transactions triggered the bank's automatic fraud detection software. I had purchased a few items from Amazon & Kindle for 2 to 3 euro each, then bought airline tickets and then wanted to book accommodation on Airbnb. The Airbnb trqansaction was denied. My bank said that that sequence of purchases was common in fraud cases so they denied it and blocked my card. They unblocked it when I assured them that all the transactions were mine.
I have also had guests who had problems with their card when booking but it was sorted in each case when I messaged them and suggested that they contact their bank.
Steve.