How to Setup Passing multiple request_params via API

I had tried creating several request params in my API that I’d like to be used to fill out all records generated. I had tried using the following POST route:

/API_NAME/&count=:count/&fein=:fein/&emp_legal_name=:emp_legal_name/&emp_addr1=:emp_addr1/&emp_addr2=:emp_addr2/&emp_city=:emp_city/&emp_state=:emp_state/&emp_zip=:emp_zip/&emp_plus4=:emp_plus4/&emp_phone=:emp_phone.custom

I had also tried using the following:

/API_NAME/:count/:fein/:emp_legal_name/:emp_addr1/:emp_addr2/:emp_city/:emp_state/:emp_zip/:emp_plus4/:emp_phone.custom

/API_NAME.custom/:count/:fein/:emp_legal_name/:emp_addr1/:emp_addr2/:emp_city/:emp_state/:emp_zip/:emp_plus4/:emp_phone

Within my Schema, I have the fields set to be Formulas that check for the presence of request_params and if blank uses a default value, but I am unsure whether I am passing the information correctly via API or if the Schema & API are getting their wires crossed?

I figure there are a couple things I am doing wrong here, but I had trouble finding more examples about using the API in this way. Any suggestions?

Cheers!