Provide payment method and place order. Provide email for guest.
Sample Curl
curl --location 'https://mygatewayurl.com/V1/storeview/default/user/quote/{guest-quote-id}/place-order' --header 'Content-Type: application/json' --data '{"email": "[email protected]","billingAddress":{"countryId":"US","regionCode":"UT","street":["22 Albert Road"],"company":"ABC","telephone":"123123213321","fax":null,"postcode":"3205","city":"South Melbourne","firstname":"Testfirst","lastname":"Testlast","middlename":null,"prefix":null,"suffix":null,"vatId":null,"customAttributes":[],"saveInAddressBook":null},"paymentMethod":{"method":"checkmo","po_number":null,"additional_data":{"amgdpr_agreement":"{}"}}}'