To get floating licenses to work, you need to make sure the client machine, where you have Mathcad running can communicate with the Flexnet license server. If you have a firewall in between, you need to add two exceptions to the list.
The default port used when contacting the license server is 7788. So that must be open, and you also need to open for the executable ptc_d.exe.
Here is what that looks like in Windows Defender Firewall
Click on Inbounds Rules
And New Rule...
Choose Port and click Next
Then choose TCP and enter 7788 in the field and click Next.
Keep the 'Allow the connection' choice and click Next
Click Next
Enter something relevant, such as Mathcad, in the Name field and click Finish.
First step is now done. Click on New Rule... again
Now select Program and click Next.
Click Browse
And find the ptc_d.exe. If this is a default installation you will find it in C:\Program Files\PTC\FLEXnet Admin License Server\x86e_win64\obj\ folder.
Click Next
Keep the 'Allow the connection' choice and click Next
Click Next
Enter something relevant, such as PTC_D, in the Name field and click Finish.
Then you are done.