You can sign up for a Sandbox Account here
After you sign up successfully, you should receive an email with instructions to create Sandbox Account on Enterprise Business Portal
If you do not receive an email,
Bank of America Merchant Services's Response code page provides
Bank of America Merchant Services's Flex Microform solution provides tools to build PCI-compliant sites and apps. To understand all of the options available to you, see our Flex microform documentation.
You are responsible for maintaining communication with Bank of America Merchant Services servers. Set your client applications that communicate with Bank of America Merchant Services to direct requests to a host name and not an IP address.