I paid with my jetBlue mastercard, no international fees.

Perhaps a phone call is worth your time to sort this out?

I had specific needs (a paid stop in St. John on the way to Nanny Cay - coming up on Monday!) - and I spoke with >4 different water taxis... I found the communication from Deane and Rachel could not have been more professional and timely. They got the job done, and their communication was as good as any vendor, anywhere.

FYI, here is an obfuscated copy of one of their emails to me...

>> To lock in a reservation, we have attached our Booking Form to complete and once this has been received and payment has been processed in full (like airline companies and travel agents), we will then send you your Booking Confirmation and further information. If you do not wish to fill out the card info on the form, please leave this blank and use this encrypted link to provide it:
>> https://priv................
>> Please kindly note that VISA or MC payments are preferred, and bookings are taken on a first come, first serve basis

And that was that.

Perhaps call them?
Tel/Whatsapp: 1-284-340-1122

HTH