Conflict between FileMaker, Big Sur and Messages?

[TayCorp]

I recently upgraded to Big Sur and I use the lasted Claris/FileMaker 19.

Since upgrading to Big Sur one of my scripts no longer works in iMessage.  

The script involved pasting several mobile numbers into iMessages via the URL Script ("iMessage://" & Filter ( Contacts::MobileGroup; "+610123456789," ). Instead of phone numbers I now only get the first record/number. Or if I do a manual copy and paste (from FileMaker to Messages I get "⬀㘀㄀㐀㈀㜀　㜀㤀㄀㌀㠀Ⰰ⬀㘀㄀㐀㐀㜀㜀㤀".

My script worked perfectly before Big Sur and was able to send texts to over fifty people at once. 

Is this a bug, a redacted feature in iMessages or a change that I need to make in FileMaker to "talk" to iMessages?

Any assistance would be appreciated

With thanks

Chris