Task: Create a contact in ActiveCampaign

n8n workflow:
{"name":"","nodes":[{"name":"On clicking 'execute'","type":"n8n-nodes-base.manualTrigger","position":[600,250],"parameters":{},"typeVersion":1},{"name":"ActiveCampaign","type":"n8n-nodes-base.activeCampaign","position":[800,250],"parameters":{"email":"","updateIfExists":true,"additionalFields":{"lastName":"","firstName":""}},"credentials":{"activeCampaignApi":"ActiveCampaign"},"typeVersion":1}],"active":false,"settings":{},"connections":{"On clicking 'execute'":{"main":[[{"node":"ActiveCampaign","type":"main","index":0}]]}}}