Cannot PUT ARCustomer with special characters in Customer ID - Sage 100

[infocynic]

Trying to do something like PUT https://example.com/AR_CUSTOMER('10;STOP&GO')

The Division is 10 and the CustomerId is STOP&GO so we need to escape that & (I cannot GET that account either, but I can find it by phone number).

With & or %26 I get a 400 Bad Request -- I think this is an IIS Error but I can't be sure. Any insights would be appreciated.