When we export a list of field names from field management under admin, we get the following:
* REST API Name
* SOAP API Names
* Friendly Names
When we are creating a custom field under field management, we need to enter the following:
* Type - string, boolean etc
* Name - this is the friendly name
* API name - is this the Rest API or SOAP API name for the field? where does the other field name go?
According to docs Create a Custom Field in Marketo - Marketo Docs - Product Docs
The automatically generated API name is used by the SOAP API and other backend processes.
And REST field name is same as API name also.