Evolution API is an open-source WhatsApp API you run yourself. Each connected WhatsApp number is an instance; paths use the instance name.
The global API key is set in your server's configuration (AUTHENTICATION_API_KEY). Send it as the apikey header. In the examples it's written {{EVOLUTION_API_KEY}}; {{EVOLUTION_HOST}} is your server.
Full reference: https://doc.evolution-api.com/
curl https://{{EVOLUTION_HOST}}/instance/fetchInstances \
-H "apikey: {{EVOLUTION_API_KEY}}"number in international format, digits only.
curl -X POST https://{{EVOLUTION_HOST}}/message/sendText/{{INSTANCE}} \
-H "apikey: {{EVOLUTION_API_KEY}}" \
-H "Content-Type: application/json" \
-d '{"number": "{{TO_NUMBER}}", "text": "Hello from PostTaco"}'